223 short cartridge length question

[Bill2905]

I have used 223 loads that were 0.020 thousandths shorter than published length. When they get to be shorter by 0.050 or more, I don't know, In general, how short can you go against published data? I'm more concerned about reduced case volume and pressure and not accuracy issues. I assume that one would start at the low end of powder charges and work up like any other load but maybe someone has some better advice.

In determining where to start with bullet seating depth, I use either a Lock N Load or a Sinclair seating depth tool. Once the approximate maximum length is determined, I test it by making up a few dummy rounds and tweaking the seating depth until I find the depth where the rifling no longer marks the bullet. Using this method, some bullets end up being seated longer than book value but they shoot fine (69 SMK and 53 V-Max are examples). The ones that concern me are those that end up being much shorter than published lengths. This is before I have even backed them off the lands by 0.020 or so. Two examples include;

The SMK 52g HPBT measures at 2.200 max length (vs. published length of 2.250). It shot fine but I stopped using it due to my hesitation over the short length.

The Hornady 52g HPBT measures at 2.173 max length (vs. published length of 2.230). In a dummy round, there was only about 0.050 of straight side remaining on the bullet after I backed it off by 0.020. I spoke with Hornady Tech service but they didn't offer much advice other than suggest there was an error in my methods. I haven't shot this load yet and am looking for advice on how to proceed or maybe just move on to a different bullet.

I use Winchester 748 for all of my 223 loads.

I have also had problems with multiple types of Hornady V-Max factory loads being too long in both of my Savage 10 223 barrels. Some were so tight the bullets were ripped out when I unloaded the rounds after realizing there was a problem.

Thanks for your help.

Bill

[CFJunkie]

Bill2905

I have to admit you have really confused me.
None of my .223s, either bolt actions or ARs, have chambers short enough to keep a 52 SMK in the brass with a 1.750 trim length if I try to measure the chamber depth.
So I am baffled that your .223 measures a shorter chamber with the 52 SMK than with the 69 SMK.

The Sierra Manual 5th edition recommends seating the 52 SMK bullets to an O.A.L. of 2.250 and the case would be trimmed to 1.750 leaving 0.500 of the bullet protruding from the brass.
The same manual recommends that you seat the 69 SMK to an O.A.L of 2.260 and the case trimmed to 1.750 leaving 0.510 of the bullet protruding from the brass.

The 52 SMK measures 0.695 base to tip and 0.332 base to ogive.

That leaves 0.363 of the bullet from the ogive to the tip.

If the 52 SMK had 0.500 sticking out of the neck there would be 0.195 seated in the neck.

So there would be 0.137 of the 0.224 body of the bullet visible in addition to the ogive to tip length.

Seating the 52 SMK at 2.200 O.A.L. would increase the length of the bullet seated in the neck to 0.245, and there would only be 0.450 of the bullet visible protruding from the brass of which .087 would be part of the 0.224 body of the bullet.

The 69 SMK measures 0.882 base to tip and 0.480 base to ogive. That leaves

0.402 of the bullet from the ogive to the tip.
Seating the 69 SMK at 2.260 and leaving 0.510 of the bullet protruding from the brass would leave 0.372 of the bullet body in the neck with 0.108 of the 0.224 body of the bullet protruding from the neck.

When I have tested my .223 rifles for chamber length, one rifle that I tested would seat the 69 SMK in the neck while the 52 SMK would be out of the neck completely.
The additional bullet body in the neck for the 69 SMK allows some of the body to remain in the neck when the ogive it touching the rifling and leaving a mark.
So I am confused that you find the 52 SMK is seating short and the 69 SMK is seating within SAAMI O.A.L. recommendations.
It is possible that your barrel might have a really short chamber.
My experience would lead me to believe that it would be just the opposite.

Maybe if you described how you are doing the seating measurements and adjustments it might help with my confusion.

[Bill2905]

CFJunkie,

It’s baffling to me as well. The measurements don’t seem believable but I have verified them with dummy rounds. My chamber comes nowhere close to fitting the SMK 52 when I test dummy rounds seated to the recommended C.O.L. It will stick in the rifling and is difficult to remove, leaving deep gouges in the jacket. I have this experience in two different Savage 223 barrels with this bullet. In both of my rifles, I tested incrementally shorter dummy rounds to arrive at a C.O.L. of 2.200".

I use a Sinclair bullet seating depth gauge to take actual measurements. If you’re not familiar with this tool, it uses the difference between two measurements;

1. The distance from a reference point to the base of a bullet inserted in the throat
   
2. The distance from same reference point to the base of a once-fired case inserted in the chamber (with the aforementioned bullet removed)

You calculate the difference between those two measurements and add it to the overall length of the bullet to come up with your C.O.L. Alternatively, you could use the bullet base to ogive measurement and calculate the cartridge base to ogive length.

I use a once-fired case from the chamber of that barrel per the instructions. I am using once-fired Federal cases that measure 1.740” on average.

I understand that this measurement is a starting point and not necessarily the law. I test the measured C.O.L. by making a dummy round at that length and chambering it. If the rifling leaves any marks I will increment down another 0.005 with a second and maybe a third dummy round until it is free of marks and assume that the exact final value is somewhere in between.

Regarding the 69 SMK, I can load that at or slightly longer than the 2.260" specification in both of my rifles using the same measurement methods.

I also load and shoot a lot of Hornady 53 gr V-Max in both rifles and am able to seat those out to 2.285” which is 0.035” over recommended C.O.L.

Last week, I shot a box of Hornady 55 gr V-Max factory loads and they were chambering hard. I forcefully unloaded a few to inspect and they were deeply gouged by the rifling.

I guess there can be infinite combinations of chamber and bullet geometries.

[Texas10]

Absolutely right about having to measure every bullet combination, every bullet lot and every chamber in case you're shooting more than one 223. I never could get the Hornaday gage to give me consistent CBTO measurements, so i changed the way i use it. I now FL size the Hornaday modified case and seat a bullet long then install on the gage. Slide it into the chamber with a firm push and retract. If it tends to stick upon retraction that is an indication that the bullet is in the lands.

I then seat the bullet .010 deeper and repeat until I find the "no stick" position. You can get the CBTO measurements down to a thou or two fairly consistently by doing this and developing a feel for the bullet touching. Best of all, if you save the case to use later as the throat erodes, and you can quantify the erosion by comparing it to rounds fired, such as .001" per 120 rounds. It's possible to predictably load further out as the throat erodes if you need to hold a seat depth for greatest consistency without having to make a new measurement.

To get that kind of accuracy in measuring CBTO you must have a good regiment for cleaning the chamber and throat. If you don't have a borescope, at least get an endoscope camera (they're inexpensive) so you can verify your cleaning methods. It's very easy to see carbon in the neck/throat/leade with an inexpensive camera.

Finally, give the Sierra p/n 1400 53 gr HP a try. You may be as delighted with its consistency as I was. It's flat based, by the way.

[CFJunkie]

Texas 10 is correct. The 53 SMK #1400 flat base bullet is very accurate in my .223s as is the Berger 52

grain

#22408 flat base.
I have heard that flat base bullet are accurate for distances under 300 yards but most of my shooting is at 100 yards at our range so they perform very well in my .223s, even the 1:9 and 1:8 twist barrels.

We are apparently using two different measurements so that may be the reason for the confusion.
I am using Overall average length (O.A.L) - measured from brass base to bullet tip, brass base to ogive length, overall average bullet length base to tip, bullet base to ogive length, and trim case length.
Most manuals provide Overall Average Length O.A.L. - bullet base to tip as their recommended seating. Sierra manuals use that length.

I measure my chambers using a Midway chamber depth gage that measures brass base to ogive to allow you to measure chamber depth directly.
You do have to be careful not to drive the bullet deep into the rifling or the chamber measures come up shorter than actual.

I remeasured the 52 and 69 SMKs with the Hornady gage I use to measure my chamber depth and got a slightly different bullet length for the base to ogive.
My last measurement were with a multi-caliber ogive length gage that apparently is slightly tighter and overstates the base to ogive length.
The difference in base to ogive length dropped from 0.332 to 0.256 with the 52 SMKs and from 0.480 to 0.395 with the 69 SMKs.

The thing that is confusing me is that chamber depth has to remain the same regardless of bullet type, assuming the bullet ogive is not being forced into the rifling to different depths. The measurements you have provided would indicate something is changing.

The thing that determines where the bullet can be seated is the position of the ogive since that is where the bullet tip finally increased to the full body diameter.
That is where the rifling can engage the bullet so if you are getting marks on the rifling, the ogive is what is showing the marks.
You can't adjust the steel in the barrel, although you can erode the rifling steel over time, especially if you load near Pmax.
The position of the ogive can be calculated and because it is in a fixed relationship to the bullet tip (+/- a few thousandths for BTHP formed bullets like the SMKs) the base to ogive measurement can be determined from the measured O.A.L.

Using the new bullet base to ogive measurements:
A 52 grain bullet seated at 2.250 O.A.L. would need a nominal chamber depth of 1.811 to just touch the rifling (a jump of 0.000).
A 52 grain bullet seated at 2.200 O.A.L. just touching the rifling would need a nominal chamber depth of 1.761. That is just 0.011 longer than the case trim.
A 69 grain bullet seated with 0.000 jump at 2.265 would have to have a chamber depth of 1.773 so we have to conclude that your chamber is at least that deep.
All of my .223 chambers are deeper than 1.800 and I regularly seat my 52 SMKs at 2.270 O.A.L.

If you can load the 69 SMK out to say 2.265 O.A.L. just touching the rifling, your chamber should be 1.778 to the rifling.
That chamber depth is still a lot shorter than any .223 chamber I have measured.
That would mean you should be able to load the 52 SMK out to 2.217 O.A.L. before they touch the rifling.
When seated at 2.200, the 52 SMK would have only 0.011 of the body available to get marks on the bullet body and the chamber would be 1.761 deep if there weren't marks.
I would think that the neck of the brass, being wider than the bullet. would be touching the chamber before that last 1/100th of an inch of the bullet body was touching the rifling.
If you are seeing marks on the 52 SMK bullet, then the bullet would have to be seated out much further than 2.200.

The 69 SMK, when seated at 2.260 in a 1.761 chamber, would have only 0.023 of the bullet body visible and the body would be 0.021 deep into the rifling if the chamber were only 1.837 deep.
But you are finding no rifling marks on the 69 SMKs at 2.260 so the chamber has to be at least 1.773 deep to not mark the 69 SMK ogive.
A 1.773 chamber depth should let you seat a 52 SMK to at least 2.212 O.A.L and allowing you to have the ogive only 0.023 out of the neck.

That's why I think there is something that doesn't compute.
There seems to be a difference between what you are measuring with the 52 SMKs and 69 SMKs and what I would conclude would be the chamber depth based upon the 69 grain SMK.
The 52 SMKs aren't very long bullets and with their boat tail they have an even shorter bullet body touching the neck.

I have heard that non-concentric seating is possible with some types of dies but I have never experienced it myself.

Is it possible that the 52 grain bullets are being seated askew slightly so the bullet is touching the rifling on only one side?
Are the rifling marks on the bullet consistent around the bullet body on the 52 SMKs?

[CFJunkie]

I started thinking about the measurements you are using.
The measure to the base of the bullet protruding from the rifling could be used to determine the ogive point on the bullet. But the bullet base to ogive measure is what would be measured if you are measuring the protruding bullet segment. That measurement, subtracted from the overall bullet length would yield the ogive to bullet tip measurement.

I don't understand the relationship to the once fired case measurement related to O.A.L since you didn't explain where the reference point might be.
Since the bullet base would have to be inserted in the neck of the brass to create neck tension, the brass length wouldn't seem to be a critical measurement unless you are measuring the maximum brass trim length the chamber would allow or if you were trying to determine the maximum shoulder of the brass the chamber would allow.
Otherwise, the brass is just along for the ride and to hold the bullet base in the neck with consistent neck tension so the bullet exit velocity doesn't vary because of varying pressure to unseat the bullet.

If the reference point is the bolt face, then the measurement from the point where the bullet is seated in the rifling to the bolt face would allow you to calculate the base to ogive measurement giving the chamber depth. That is what the Midway gages allow you to measure directly. The one thing I have found is that providing too much pressure on seating the bullet can cause deeper than actual chamber measurements.
The brass itself isn't critical to any of the ogive measures unless the brass shoulder or neck trim limits are exceeded.
Using once fired brass might create some minor variation if you are full resizing your brass before reloading which could set back the shoulder and might allow the brass to seat deeper.
If you are neck sizing only, it probably won't make a difference.

The brass base to ogive measurement (also the bolt face to ogive measurement) plus the bullet tip to ogive measurement would provide the O.A.L. measurement, providing you are using the same gage to set the base to ogive measurement and to measure the bullet base to ogive measurement.
The overall bullet length minus the bullet base to ogive measurement provides the bullet tip to ogive measurement.

Just for the record, I actually measure all my reloads from base to ogive to eliminate the variation in bullet tips that are caused by swaging the jackets on BTHP bullets like the SMKs.
I normally load to +/- 0.001 inch standards across 100 reloads.
To set my dies, I also check the O.A.L. as well before I start loading and record it so I know what the O.A.L. measurement is for each load.

As I reported in my last post, I found two types of gages produced different base to ogive measures and so I reverted to my Midway gage to measure bullet base to ogive, just like I use when I am reloading.

Incidentally, one of my .223 bolt actions has a chamber so deep that a 52 SMK bullet seated in the rifling has none of the bullet body still in the case when the measurement is taken.
Measuring the brass length under those conditions means nothing to the overall chamber depth as that chamber is longer than the brass length and the total bullet length of a 52 SMK.

[Bill2905]

I check cartridge base to ogive length on all loaded rounds as well. I have found enough variation in bullet lengths to warrant it since I’m not loading large quantities.

The reference point I mentioned with the Sinclair tool is the rear surface of a jig that inserts into the back of the receiver. You can probably find a demo on YouTube that will explain it better than I can.

Interesting that you mentioned concentricity. I have noticed with my dummy rounds that as I go shorter and approach the point where the rifling marks disappear, the marks are not uniform around the bullet but more to one side. I use standard Lee dies. There are probably better bullet seating products out there, I just haven’t evolved to that level yet.

It’s apparent that we use different methods although we probably arrive at similar conclusions. I will re-examine mine with the advice that has been given.

I arrived at the following maximum lengths for the two SMK bullets in question;

SMK 52 - Max cartridge length = 2.200
SMK 52 - Max cartridge base to ogive length = 1.854

SMK 69 - Max cartridge length = 2.260
SMK 69 - Max cartridge base to ogive length = 1.875

I loaded up a few yesterday with minimum charges and went to the 100 yd range.

SMK 52 - 25.0 gr W748, Rem 7-½ primer, Starline case, seated at 2.180 COL (0.020 off the lands). Cases and primers looked good after firing with easy extraction. Groups were 0.5” or less.

SMK 69 - 24.0 gr W748, Rem 7-½ primer, Starline case, seated at 2.245 COL (0.015 off the lands). Cases and primers looked good after firing with easy extraction. Groups were 0.5” or less.

I didn’t take my chronograph because it’s been acting up lately.

Back to what I was originally asking in a roundabout way - Is it reasonable to try these shortened loads using some caution? Or, would you just avoid it all together and move on to other bullets and loads that better conform to published specs?

[CFJunkie]

If you're getting tight groups, there are no signs of pressure on the primers and cases extract, you shouldn't be worrying.
Seating deeper by 0.050 would increase pressure by about 1640 psi but you're already compensating for that by loading light at about 42954 psi against a Pmax of 55,000 psi.
QuickLOAD says that with a trim length of 1.750, you could load up to 26.8 grains of W748 behind the 52 SMK and still be just under PMax at 70 deg. F. If your shooting in colder conditions, you have even more margin.
For the 69 SMK, the 24.0 grain load is at 51,137 psi so you are closer to Pmax and can only get to 24.5 grain charge before you exceed it.
I think your 24.0 grain charge might be right in the sweet spot.
For your 52 SMK loads, a 26.3 grain charge of W748 would put your 52 gr SMK load in about the same pressure range as the 69 SMK load.

I think I figured out the difference in our measurements.
I used O.A.L. at 2.200 for the 52gr SMK and you did too, but your COL measurement was 2.180 (0.020 off the lands). Base to Ogive = 1.854 which would mean your chamber was 1.874.
I used O.A.L. at 2.260 for the 69 gr SMK and you did too, but the COL measurement was 2.245 (0.015 off the lands). Base to Ogive = 1.875 which would mean your chamber was 1.890.
Both of those measures seem to be a bit longer than I would have suspected.
It is possible that the tool you are using to measure the ogive might be a bit tighter than mine.
I calculated that your tools are measuring the base to bullet ogives a bit longer (0.017) than my multi tool and much longer than my Hornady tool.
(As I mentioned in my last post, I use the Midway (Spring River) tool to measure base to ogive when I am reloading so I trust it to measure bullet base to ogive as well.
The multi-caliber tool that I have isn't used for chamber or bullet measurements, but it was handy.)
The difference I think comes from your tool measuring 0.102 longer base to ogive for the 52 SMK and 0.054 longer base to ogive for the 69 SMK compared to the Midway tool.
The difference with the multi-tool is a constant 0.017 longer which makes me think that the two bullets have a slightly different shape from ogive to the tip and are quite different as they approach the ogive. That might be creating the difference in the measurements.

I would predict that for the 52 SMK there to be just over 0.1 inches of bullet body visible sticking out of the neck and there to be a total of 0.450 of the bullet poking out of the brass.
There should be 0.510 of the 69 gr SMK sticking out of the brass.