Since many of you have shown interest in the data for my .223 and 6.5mm CM rifles, I thought I might also amass some data for my two .308 Savages Model 10 LE rifles, as well.
I apologize, in advance, for the long post, but I wanted to give you all the similarities and commonalities of the two rifles so you can make conclusions on how my results might apply to your rifles.
If felt that posting the data for each rifle separately would make it more difficult to compare the results considering these rifles are both .308s.
PLEASE NOTE: The data presented is for two particular rifles with 24-inch Savage barrels and the results show that barrels have preferences.
Any other rifle barrel may or may not produce similar results.
However, the data provides information on powder and bullet performance that might be of help and provide some ideas for .308 reloaders.
Background:
My two .308 Savages are both Law Enforcement models.
The 10 FP .308 is a 2008 model with 24-inch 1:10 twist barrel with an Accu-trigger, and a hidden magazine stock, similar to the one that comes on the 12 FVs. The stock has no strengthening element and is subject to flexing.
I shot 6,500 rounds through the 10 FP rifle as I was learning to reload and finding out what the rifle liked,
Eventually the erosion of the lands and the subsequent seating out to keep the jump around 0.020 caused a drop in group averages around 6,200 rounds, probably due to inconsistent neck tension with less and less bullet body in the neck. My groups grew by about 0.2 inches on average.
I was somewhat inexperienced with chamber erosion and took about 300 more rounds to realize that it was not me but the rifle losing accuracy and it wasn’t getting any better.
I bought a 10 FCP-K .308 as a replacement when I was deciding whether to replace the barrel the 10 FP.
The 10 FCP-K came with a fluted, 24-inch 1:10 twist barrel fitted with a muzzle brake mounted in an Accu-stock with a detachable mag.
I had the 10 FP rebarreled by Savage in 2013 with a 24-inch fluted, 1:10 twist target Savage barrel. After it was rebarreled, I replaced the original stock with a Bell & Carlson adjustable stock because I had become aware that the original stock was a bit too short for me.
The adjustable B&C stock had an aluminum strengthener so, as an added advantage, it also eliminated flex in the factory stock.
Both rifles have their Varmint/Target Accu-triggers set at 2 lbs.
Both rifles now have NightForce 8-32x56mm Benchrest scopes mounted on Burris Signature Zee rings.
The 10 FCP-K has a Mil Dot reticle and the 10 FP has a NP2-DD reticle.
When I got my rebarreled 10 FV back from Savage, I wound up with two .308 rifles with new barrels but I also had about 5 years of reloading data for .308s based upon the lessons learned shooting my original 10 FP barrel.
One thing I quickly determined is that the two new barrels were slightly different when it came to bullet weight preferences.
You also will probably note looking at the data below that the best load velocities for the 10 FP are slightly faster than the 10 FCP-K.
The 10 FCP-K has a 2.125-inch muzzle brake (from the factory) which changes the reflection time for the barrel & muzzle brake and, therefore, increases the exit time for the bullet in order to match the point when the reflection is at the chamber (keeps the crown tight and minimizes harmonics). I reduce the charges in the 10 FCP-K to slow the exit time to account for the added reflection through the muzzle brake (except for the last pass down the barrel to the muzzle since there is no rifling in the muzzle brake and the added muzzle brake reflection doesn’t matter).
I have found that each rifle’s best performance occurs when the bullet exits within +/- 0.003 msec of the calculated exit time for its barrel, and in the case of the 10 FCP-K, its muzzle brake (+/- 0.003 msec. of exit time equates to about 0.1 grains of powder).
Results for Powder-Bullet Combinations
The following tables show the average performance for each Powder-Bullet combination shot with each rifle and also shows the best load average and the best load velocity.
All the data summarized below is for 5-round groups shot at 100 yards at a range that is 250 ft above sea level in Northern Virginia.
The data for each combination is an average for all seating depths and powder charges for the groups shot with each particular combination.
I have found that the combination average gives a very useable representation of what powders and bullets work best for my rifles.
The best loads show what might be achieved by tuning for a particular powder bullet combination in a specific barrel.
10 FP (New Barrel) .308 (Law Enforcement Model) - 5-round Groups
By Weight
# Grps -- Powder ---------Bullet --------- Wgt. – Avg. -- Best Load – Vel. – Weight Avg.
---17-------IMR4064—Sierra TMK #7755----155---- 0.373 ------ 0.306------2598
---16-------IMR4166—Sierra TMK #7755----155---- 0.392 ------ 0.338------2560 ---- 0.403 - 155 grs
---28------- H4895 --- Sierra TMK #7755----155---- 0.430 ------ 0.429------2633
---16------- N140 ---- Sierra TMK #7755----155---- 0.415 ------ 0.345------2604
---4------- IMR4166— Sierra SMK #2000----168---- 0.327 ------ 0.327------2544
---4 ------- N140 ---- Sierra SMK #2000----168---- 0.348 ------ 0.348------2568
---47----- IMR4064— Sierra TMK #7768----168---- 0.455 ------ 0.413------2546 ------ 0.412 - 168 grs.
---24----- IMR4166— Sierra TMK #7768----168---- 0.443 ------ 0.399------2522
---22---- H4895 ----- Sierra TMK #7768----168---- 0.462 ------ 0.363------2599
---9------ N140 ------ Sierra TMK #7768----168---- 0.436 ------ 0.387------2547
---7 ----- IMR4064 — Sierra TMK #7775----175---- 0.455 ------ 0.403------2546
---2 ---- IMR4166 -— Sierra TMK #7775----175---- 0.475 ------ 0.475------2509 ------- 0.469 – 175 grs.
---5 ----- H4895 ----- Sierra TMK #7775----175---- 0.477 ------ 0.477------2583
-207 –Total Grps. -------------------------- Average –0.431
By bullet weight average, the 10 FP (New barrel) seems to perform slightly better with 155 grain bullets than 168 grain bullets and significantly better than 175 grain bullets.
By Average
# Grps -- Powder ---------Bullet --------- Wgt. – Avg. -- Best Load – Vel. --Rank
---4------- IMR4166—Sierra SMK #2000----168---- 0.327 ------ 0.327------2544 -- 1
---4 ------- N140 ---- Sierra SMK #2000----168---- 0.348 ------ 0.348------2568 -- 2
---17-------IMR4064—Sierra TMK #7755----155---- 0.373 ------ 0.306------2598-- 3
---16------IMR4166 —Sierra TMK #7755----155---- 0.392 ------ 0.338------2560-- 4
---16------- N140 ---- Sierra TMK #7755----155---- 0.415 ------ 0.345------2604-- 5
---28------ H4895 --- Sierra TMK #7755----155---- 0.430 ------ 0.429------2633-- 6
-----9------ N140 ---- Sierra TMK #7768----168---- 0.436 ------ 0.387------2547-- 7
---24---- IMR4166 -—Sierra TMK #7768----168---- 0.443 ------ 0.399------2522-- 8
---7 ----- IMR4064 -—Sierra TMK #7775----175---- 0.455 ------ 0.403------2546-- 9
---47---- IMR4064 -—Sierra TMK #7768----168---- 0.455 ------ 0.413------2546-- 10
---22---- H4895 ----- Sierra TMK #7768----168---- 0.462 ------ 0.363------2599-- 11
---2 ---- IMR4166 -— Sierra TMK #7775----175---- 0.475 ------ 0.475------2509-- 12
---5 ----- H4895 ----- Sierra TMK #7775----175---- 0.477 ------ 0.477------ 2583-- 13
-207 –Total Grps. -------------------------- Average –0.431
Looking at rankings by average, the 10 FP (New Barrel) rifle seems to prefer the 168 grain bullets with IMR4166 and N140 powder (averages of 0.327 and 0.348 ranking #1 & #2 but the # groups is a small sample). The analysis of the top 25 loads, listed below, gives a slightly different perspective.
But the H4895 and IMR 4064 powders (rank #10 & #11) did not perform as well with the 168 grain bullets (averages of 0.436 and 0.443).
However, the 155 grain TMK bullets hold the #3 through #7 rankings with 4 different powders and much more statistically significant samples.
The 155 grain TMK bullets performed better (averages from 0.392 to 0.430) with all powders compared to the 175 grain TMK bullets (averages from 0.455 to 0.477).
By Powder
# Grps -- Powder ---------Bullet --------- Wgt. – Avg. -- Best Load – Vel.- Pwdr. Avg.
---28------- H4895 --- Sierra TMK #7755----155---- 0.430 ------ 0.429------2633
---22----- H4895 ----- Sierra TMK #7768----168---- 0.462 ------ 0.363------2599 --- 0.447 - H4895
---5 ------ H4895 ----- Sierra TMK #7775----175---- 0.477 ------ 0.477------2583
---17-------IMR4064—Sierra TMK #7755----155---- 0.373 ------ 0.306------2598
---47------ IMR4064— Sierra TMK #7768----168---- 0.455 ------ 0.413------2546 -- 0.429 – IMR4064
---7 ------- IMR4064 — Sierra TMK #7775----175---- 0.455 ------ 0.403------2546
---4------- IMR4166— Sierra SMK #2000----168---- 0.327 ------ 0.327------2544
---16-------IMR4166—Sierra TMK #7755----155---- 0.392 ------ 0.338------2560 – 0.417 – IMR4166
---24----- IMR4166— Sierra TMK #7768----168---- 0.443 ------ 0.399------2522
---2 ---- IMR4166 -— Sierra TMK #7775----175---- 0.475 ------ 0.475------2509
---4 -------- N140 ---- Sierra SMK #2000----168---- 0.348 ------ 0.348------2568
---16------- N140 ---- Sierra TMK #7755----155---- 0.415 ------ 0.345------2604 – 0.412 – N140
---9------ N140 ------ Sierra TMK #7768----168---- 0.436 ------ 0.387------2547
-207 –Total Grps. -------------------------- Average –0.431
Note: For H4895 and IMR4064 powders, the averages are sorted by weight from 155 to 175.
IMR4166, with the second-best overall average, follows that weighting order sorting with the exception of the small sample of 168 SMK bullets.
N140 powder, with the best overall average, follows the IMR4166 sequencing except that there were no groups shot with 175 grain bullets.
However, it should be noted that no 175 grain bullets were shot with N140, so the average is slightly skewed to the low side.
10 FP – Best 25 Loads
By Weight
# Grps -- Bullet ----------------- Wgt. – Avg. -- Median - St Dev
----39 ----- Sierra TMK #7755 – 155 – 0.349 – 0.337 ---- 0.044
---- 8 ----- Sierra SMK #2000 – 168 – 0.337 – 0.344 ---- 0.047
--- 21 ----- Sierra TMK #7768 – 168 – 0.378 – 0.385 ---- 0.039
--- 66 ------------------------------ 0.360 – 0.357 ---- 0.044
By Average
# Grps -- Bullet ----------------- Wgt. – Avg. -- Median – St Dev
---- 8 ----- Sierra SMK #2000 – 168 – 0.337 – 0.344 ---- 0.047
---39 ----- Sierra TMK #7755 – 155 – 0.349 – 0.337 ---- 0.044
--- 21 ----- Sierra TMK #7768 – 168 – 0.378 – 0.385 ---- 0.039
--- 66 ------------------------------ 0.360 – 0.357 ---- 0.044
Note that the accuracy for the 8 groups of 168 SMK bullets is about 0.012 smaller than the 39 groups of the 155 TMK bullets.
However, the best three loads are with 155 TMK bullets and average 0.311 followed by a load of 168 SMKs at 0.327.
Also, 8 of the top 10 loads were shot with 155 TMK bullets and average 0.334 overall with a total of 23 groups.
The other two loads were 168 SMKs (the only two shot with 168 SMKs to date) with an overall average of 0.337 with a total of 8 groups.
Since the Top 25 loads contain 6 additional loads (#s 11,12, 14, 18, 19, and 21), the top 25 average tends to mask the best performance of 155 grain TMKs.
The best 175 grain load was ranked #67 overall.
10 FCP-K .308 (Law Enforcement model) – 5-round Groups
Note that the number of 155 grain bullet samples is quite small primarily because I abandoned the 155 grain bullets pretty quickly after I confirmed the performance was lacking compared to the heavier weight bullets.
I had shot a lot of 150 and 155 grain bullets prior to switching to exit time reloading so I didn’t waste time and money hoping for miracles once I had established that this barrel prefers bullets from 168 to 175 grains.
By Weight
# Grps -- Powder ---------Bullet --------- Wgt. – Avg. -- Best Load – Vel. – Weight Avg.
---- 3------- H4895 ----Sierra TMK #7755----155---- 0.466 ------ 0.400------2498
---- 4-------IMR4064—Sierra TMK #7755----155---- 0.430 ------ 0.430------2467 ---- 0.455 - 155 grs
---- 4------- H4895 --- Sierra SMK #2000----168---- 0.394 ------ 0.394------2468
---29------ IMR4064 -- Sierra TMK #7768----168---- 0.428 ------ 0.349------2385
---- 5------ IMR4166 -- Sierra SMK #7768----168---- 0.398 ------ 0.378------2385------ 0.428 - 168 grs.
---- 1------- H4895 ----Sierra TMK #7768----168---- 0.446 ------ 0.446------2453
--- 33-------- N140 ---- Sierra SMK #7768----168---- 0.471 ------ 0.283------2413
--- 4------- H4895 ----Sierra SMK #2275----175---- 0.324 ------ 0.324------2445
---11------ IMR4064— Sierra SMK #2275----175---- 0.372 ------ 0.347------2434
-----5----- IMR4166— Sierra SMK #2275----175---- 0.361 ------ 0.361------2380
-----4----- N140 ------ Sierra SMK #2275----175---- 0.370 ------ 0.363------2404
---81 --- IMR4064 ---- Sierra TMK #7775----175---- 0.428 ------ 0.295------2417
---22 --- IMR4166 --— Sierra TMK #7775----175---- 0.413 ------ 0.336------2356 ------- 0.394 – 175 grs.
---42 ------ H4895 ---- Sierra TMK #7775----175---- 0.453 ------ 0.316------2429
---34 ------ N140 ------ Sierra TMK #7775----175---- 0.428 ------ 0.322------2391
---17 ------ H4895 ---- Sierra TMK #7795----195---- 0.446 ------ 0.367------2382
-----3 --- IMR4166 -— Sierra TMK #7795----195---- 0.421 ------ 0.421------2331------- 0.430 – 195 grs.
-----3 ------ N140 ----- Sierra TMK #7795----195---- 0.423 ------ 0.423------2344
-298 –Total Grps. -------------------------- Average –0.431
From the overall average by bullet weights, the 175 grain bullets, particularly the 175 gr SMKs, seem to perform the best in this rifle.
The 195 TMKs have a very slight edge over the 168 grain TMKs. The small sample of 168 SMKs out-perform both.
By Average
# Grps -- Powder ---------Bullet --------- Wgt. – Avg. -- Best Load – Vel. – Rank
--- 4------- H4895 ----Sierra SMK #2275----175---- 0.324 ------ 0.324------2445 ----- 1
-----5----- IMR4166— Sierra SMK #2275----175---- 0.361 ------ 0.361------2380 ---- 2
---22------ N140 ------ Sierra SMK #2275----175---- 0.370 ------ 0.363------2404 ---- 3
---11----- IMR4064 — Sierra SMK #2275----175---- 0.372 ------ 0.347------2434 ---- 4
----- 4------ H4895 --- Sierra SMK #2000----168---- 0.394 ------ 0.394------2468 ---- 5
---- 5----- IMR4166 -- Sierra SMK #7768----168---- 0.398 ------ 0.378------2385 ---- 6
---22 ---- IMR4166 -— Sierra TMK #7775----175---- 0.413 ------ 0.336------2356 ---- 7
-----3 ---- IMR4166 — Sierra TMK #7795----195---- 0.421 ------ 0.421------2331 ---- 8
-----3 ----- N140 ----- Sierra TMK #7795----195---- 0.423 ------ 0.423------2344 ---- 9
---34 ----- N140 ------ Sierra TMK #7775----175---- 0.428 ------ 0.322------2391 --- 10
---81 --- IMR4064 ---- Sierra TMK #7775----175---- 0.428 ------ 0.295------2417 --- 11
---29------ IMR4064 -- Sierra TMK #7768----168---- 0.428 ------ 0.349------2385 --- 12
---- 4------IMR4064-- Sierra TMK #7755----155---- 0.430 ------ 0.430------2467 --- 13
---- 1------- H4895 ----Sierra TMK #7768----168---- 0.446 ------ 0.446------2453 --- 14
---17 ------ H4895 ---- Sierra TMK #7795----195---- 0.446 ------ 0.367------2382 --- 15
---42 ------ H4895 ---- Sierra TMK #7775----175---- 0.453 ------ 0.316------2429 --- 16
--- 3-------- H4895 ----Sierra TMK #7755----155---- 0.466 ------ 0.400------2498 --- 17
--- 33------- N140 ---- Sierra SMK #7768----168---- 0.471 ------ 0.283------2413 --- 18
-298 –Total Grps. -------------------------- Average –0.431
The 10 FCP-K rifle prefers 175 grain SMK bullets (holding the top 4 places in the table with 4 different powders with averages between 0.324 and 0.370)
The next two places go to 168 grain bullets (1 SMK with H48985 and 1 TMK with IMR4166) with averages of 0.394 and 0.398.
The 175 grain TMK bullets averaged from 0.413 to 0.466.
The 195 grain TMKs averaged from 0.421 to 0.446.
By Powder by Average
# Grps -- Powder ---------Bullet --------- Wgt. – Avg. -- Best Load – Vel. – Powder Avg.
---- 4-------- H4895 --- Sierra SMK #2000----168---- 0.394 ------ 0.394------2468
--- 4-------- H4895 ----Sierra SMK #2275----175---- 0.324 ------ 0.324------2445
---17 ------ H4895 ---- Sierra TMK #7795----195---- 0.446 ------ 0.367------2382---- 0.441 – H4895
---- 1------- H4895 ----Sierra TMK #7768----168---- 0.446 ------ 0.446------2453
---42 ------ H4895 ---- Sierra TMK #7775----175---- 0.453 ------ 0.316------2429
---- 3------- H4895 ----Sierra TMK #7755----155---- 0.466 ------ 0.400------2498
---- 4-------IMR4064—Sierra TMK #7755----155---- 0.430 ------ 0.430------2467
---29------ IMR4064 -- Sierra TMK #7768----168---- 0.428 ------ 0.349------2385
---11------ IMR4064— Sierra SMK #2275----175---- 0.372 ------ 0.347------2434------ 0.423 – IMR4064
---81 ----- IMR4064 --- Sierra TMK #7775----175---- 0.428 ------ 0.295------2417
-----4----- IMR4166— Sierra SMK #2275----175---- 0.361 ------ 0.361------2380
---- 5----- IMR4166 -- Sierra SMK #7768----168---- 0.398 ------ 0.378------2385 ------- 0.406 – IMR4166
---22 --- IMR4166 -— Sierra TMK #7775----175---- 0.413 ------ 0.336------2356
-----3 --- IMR4166 — Sierra TMK #7795----195---- 0.421 ------ 0.421------2331
---- 4------ N140 ----- Sierra SMK #2275----175---- 0.370 ------ 0.363------2404
-----3 ----- N140 ----- Sierra TMK #7795----195---- 0.423 ------ 0.423------2344------- 0.430 – N140
---34 ----- N140 ------ Sierra TMK #7775----175---- 0.428 ------ 0.322------2391
--- 33------N140 ------ Sierra SMK #7768----168---- 0.471 ------ 0.283------2413
-298 –Total Grps. -------------------------- Average –0.431
The 10 FCP-K rifle also seems to prefer IMR4166 powder followed by IMR4064 powder based upon the average ranks.
Also note that N140 powder didn’t perform well with the 168 grain bullets (rank #17) although it did produce a best load under .300 inches.
10 FCP-K – Best 25 Loads
By Weight
# Grps -- Bullet ----------------- Wgt. – Avg. -- Median – St Dev
--- 13 ---- Sierra TMK #7768 – 168 – 0.336 – 0.335 ---- 0.035
--- 15 ---- Sierra SMK #2275 – 175 – 0.351 – 0.350 ---- 0.052
--- 32 ---- Sierra TMK #7775 – 175 – 0.337 – 0.337 ---- 0.049
---- 1 ---- Sierra TMK #7795 – 195 – 0.367 – 0.367 ---- ----
--- 65 ----------------------------- 0.342 – 0.346 ---- 0.049
By Average
# Grps -- Bullet ----------------- Wgt. – Avg. -- Median – St Dev
--- 13 ---- Sierra TMK #7768 – 168 – 0.336 – 0.335 ---- 0.035
--- 32 ---- Sierra TMK #7775 – 175 – 0.337 – 0.337 ---- 0.049
--- 15 ---- Sierra SMK #2275 – 175 – 0.351 – 0.350 ---- 0.052
---- 1 ---- Sierra TMK #7795 – 195 – 0.367 – 0.367 ---- ----
--- 65 ------------------------------ 0.342 – 0.346 ---- 0.049
Note that the difference between the accuracy of the 168 TMK and 175 TMK loads, accounting for 45 of 65 groups, are within 0.001 inches.
That would tend to indicate that there is very little difference in the rifle’s preference for the two bullets but averages can be deceiving.
The top 10 loads include 175 TMK bullet loads in position # 2,3,5, 7, 8 & 10 with a total of 13 groups and an average of 0.312.
168 grain TMK bullet loads average 0.295 and occupy position #s 1 & 4 but with a very small sample of groups (2), and 175 grain SMK bullets occupy position # 9 with 4 groups (0.324).
Summary:
The overall 5-round group averages for the two rifles are within 0.0007 inches for 207 and 298 groups for the 10 FP and 10 FCP-K respectively making the results just about dead even when all recorded rounds are considered.
The 10 FCP-K rifle has two best loads that are under 0.300 inches while the 10 FP has its smallest best load average at 0.306.
The averages for the 25 best groups show a slight advantage (0.018) for the 10 FCP-K for about the same number of groups.
The Medians for the 25 best groups have a smaller advantage (0.011) for the 10 FCP-K.
The standard deviation is slightly larger by 0.0011 for the 10 FCP-K but that difference is also inconsequential.
The two rifles are incredibly similar in accuracy but their best accuracy occurs with different weight bullets.
Interestingly, I recently began shooting each of these again because I have lots of .308 powders, large rifle primers, and .30 caliber bullets so I decided to shoot the two old .308s rather than my newer .223 and 6.5mm CMs so I could save some of the reloading supplies for the rifles I have been shooting a lot because their reloading supplies were in shorter supply in my stash.
Both of these .308 rifles have been well used.
The 10 FP has shot over 3900 rounds through its replacement barrel and the 10 FCP-K has shot over 4400 rounds through its original barrel.
Just about all of the loads have been tuned to optimum exit time, so they are not even close to Pmax pressures.
You can tell that from the muzzle velocities of the best loads.
For those who would presume that these two well used barrels are shot out, here is something to consider.
The average group size for the last 4 loads for the 10 FP, using 155 TMK bullets and IMR4064 powder, averaged 0.355 with the best load averaging 0.306, the smallest load average it has ever shot.
The 10 FCP-K shot its last 4 loads with 175 TMK bullets and IMR4064 powder to an average of 0.334 with its best load averaging 0.295, the second-best load it has ever shot.
For everything that I see, they both seem to be shooting as good as they have ever shot.
Other potential sources of inaccuracy:
It is probable that the accuracy of each rifle is limited by the shooter’s capabilities as well.
Those familiar with the performance of my 12 FV rifles in .223 and 6.5mm Creedmoor calibers have probably noted that I performed best with the lowest caliber rifle and that these two .308s with a higher caliber have the largest average but almost identical group sizes.
The heavier recoil may be the factor expanding group size as caliber increases.
It would be interesting to find out whether other shooters note the same average group size growth.
If they don’t, it probably is a reflection of my problems with maintaining accuracy with increasing recoil.
Reply With Quote
Originally Posted by charlie b
Bookmarks