Reply With QuoteGo in between the two pictures. As deep as you can but stay above the donut area at the neck/shoulder junction.
John
I just ordered my first custom barrel. I ordered a Shilen Stainless Select Match. While placing my order NSS informed me that Shilen offers for no additional cost the option to send in a dummy round which is used to customize the chamber (http://www.shilen.com/faq.html#question3)
After much searching I can't find discussions where others are talking about this and honestly have no idea if this is something I should be doing or not. I shoot mostly at 100 yards for groups but mostly just to develop loads for shooting at 1,000 yards. My primary bullet is the 175gr SMK but also want the option to shoot 178gr A-Max, and 168gr/185gr Berger Target Hybrids.
I am leaning toward just having Shilen send me whatever they typically do which I would guess should be pretty good for my purposes. While not extremely long, my selected bullets are on the long side. I imagine I will be able to reach the lands with any of these bullets.
If the recommendation is to have the chamber customized then I would ask for guidance of the seating depth on the dummy rounds I should be providing to Shilen. I have heard before that you want to seat so that the bearing surface is at least one caliber into the neck. Does this mean 1) the bearing surface should be seated into the neck (second picture) or 2) the overall length which should be seated into the neck (first picture).
As always, any advice is appreciated.
Go in between the two pictures. As deep as you can but stay above the donut area at the neck/shoulder junction.
John
Hondo, does that mean you would recommend that I send Shilen the dummy rounds loaded in such a way rather than having them cut it "stock"?
I didn't see where you specified what cartridge you are chambering for so my statement is based on this.
It's been my experience that often times a SAAMI spec chamber will have a throat that exceeds magazine length for optimum seating depth. This is not always the case, but it is very common. As an example I have a .300 win mag with a spec chamber in a Savage action. If I seat a 175 Barnes LRX to touch the lands (which this barrel really likes), the cartridge will not fit in the magazine.
So, my advice is to take their advice. Decide what sort of bullet you want to use, seat a dummy to a length that functions well in your magazine (hopefully somewhere near SAAMI max OAL) and send it to them. When you get your barrel, make sure to work your load up from recommended starting. It's been my experience that a shorter throat will take less powder to achieve higher pressures.
Good luck. Tell us how it works out!
mjphawk:
Well done to send the diagram. I don't know I have seen that issue, I just got a 30-06 Bull from them and went with their standard.
Rather than split the difference, a thought would be to go a bit shorter.
As the throat wears, you can then extend the seating and still chamber. If you shoot a lot you will erode the thoart enough to see in 5k and maybe enough to affedc things by 8k. Its amazing how fast 5k can go!
On the other hand, when I am doing what you do at 100 yds, I just single load anyway.
gblyer, I am shooting a 308 WIN. The carrier in my magazine is 3-inches, so I will be able to accommodate COALs in excess of maximum SAMI specs (2.810") by a reasonable margin. The length from the beginning of the boat-tail / bearing surface junction to the tip of the meplat is the same for the 175 SMK / 168 SMK / and 168 Berger Hybrid (1.060"). The 175 Berger VLD and 185 Berger Hybrid are longer at 1.128" and 1.215", respectively. If I were to load up 175 SMKs at max SAMI length (2.810") that would mean the 185 Hybrid (which is 0.155" longer) would be at 2.965" COAL if seated the same depth into the cartridge. This assumes the datum line is at the same place on each of these projectiles which I know isn't necessarily the case. Seems if I am going to send them dummy rounds I am best off optimizing for the bullet I use most and hoping for the best on some of the longer bullets I have no experience with. Worst case I single load. The 168 Hybrid has better ballistics than the 175 SMK anyhow so I don't know that I would ever need to go heaver.
I'm probably going to call Shilen on Tuesday and talk to them a bit as well. Their site states that if a customer has any questions they should call and I figure they are probably in a good position to provide advice on what works with their barrels.
Yes call the pros for sure. They know what they're doing. Your thinking is sound in accommodating for the most used bullet.
I've had good luck with an Obermeyer 308 chamber with 168-178 AMAX.
Thanks. I figure I want to hear what Shilen says. As per the advice I got on another thread, I don't want to "customize" something that doesn't need to be messed with and end up screwing myself up. I am still hoping to hear from some of the folks with Shilen barrels to see what they did and what their results were.Originally Posted by gbflyer
Keep in mind, most any barrel maker will do the same, if you ask them.
I'm sure. This is my first re-barrel and am new to this game. I didn't even know this was something that could be customized, let alone being prepared for how to answer if or how I wanted it customized.
Next time I hope to be having a custom gun maker using their knowledge to make these decisions for me!
shilen is going to tell you to send dummy rounds....ive shot 5 shilen barrels and had the same conversation when i ordered my first barrel from them...just an FYI...they are great PPL but they are busy and get asked the same questions daily so they are short when you talk to them....not rude just short.
if you plan to shoot the berger hybrids and or VLDs they are probable the longer of the bullets your looking at shooting so id take the bullet with the longest ogive to meplat measurement and use it as my dummy round...seat it at mag length plus 0.030 to 0.040 deeper so you can chase the lands as the throat wares...the other bullets you mention should seat deeper because the the ogive will be closer to the meplat of the bullet...you can easily check by getting a box of each bullet seat all of the bullets with the same measurement to the ogive and then measure the over all length.
I will check my clearance in my 30-06 Shilen, I am just single loading as its bench rest and I don't like to struggle with the magazine (new and Savage is not a great feed setup, worth it for hunting but not bench)
I am not going any longer than 175 so probably have latitude and the ELD types might be a problem.
Yes. You don't want the gas ring to go in past the neck/shoulder junction if you can help it. You really need to decide what bullets you will optimize for. Yes, you can seat a heavy bullet deep into the case, but you'll sacrifice case volume and the gas ring will be too deep. Or, you can seat a light bullet very shallow so it's just barely holding on by it's finger nails, so to speak, so that you can get it closer to the lands if that's where it shoots best. If your particular caliber offers very light and very heavy bullets you can't really optimize for both even though you may be able to shoot both. So pick what bullets you think you'll be using for serious precision shooting and use those when you make up your dummy rounds.
Make a couple of dummy rounds with different bullets and measure the base to ogive distance. You may surprise yourself and find that a lighter bullet might just measure a bit longer than a heavy one with a different shape. I just finished reaming the throat of a new barrel (not a Shilen) and measuring CBTO distances for 8 common .223 bullets I have on hand when they're touching the lands. I used a Hornady comparator. The 77gr SMKs measured shorter than the Berger 70gr VLDs. So don't assume the heaviest bullet will be the longest.
After you finish measuring and finding the longest CBTO of your favorite bullets when they're seated at a reasonable depth, then make two dummy rounds with extra neck tension and send them to Shilen. That's what I did when I ordered my last Shilen barrel. Be sure to send two in case they drop one and it lands on it's nose. Pack them carefully.
Later on if you find that you want to use very long and heavy bullets, you can always buy a throating reamer for about a hundred and a half and extend the throat. You might also want a longer throat if testing shows that your favorite bullets prefer a really long jump. It's easy, but be careful.......... you can't go back.
Thanks LongRange. Your proposal makes a lot of sense. I took some measurements today and will need to wait for the Bergers to arrive in the mail to take some more . At this point I think I am going to ignore the 185gr Hybrid since I'm thinking it doesn't make sense to customize my gun based on a bullet I may never use (I can load them deep).
Is there a generally accepted "ideal" seating depth? If I were to design the chamber around a single projectile, how would I do that given that my magazine allows me to load significantly over SAMI specs which gives me quite a bit of flexibility.
just curious why you think its a bad thing for the gas ring to be in the case?
i had a shilen 260 barrel chambered with .240 free bore so i could load a full case of H4831sc with a 142g smk without compressing...this put the gas ring just above the neck/should junction and worked out great for the first 800-1000 rounds...as the throat got longer and the bullet moved farther outta the case my ESs started going through the roof...it took me a minute to figure it out but it ended up being not enough bullet in the neck.
the last barrel i had chambered in 260(in my safe as i type with 219 rounds through it)is chambered with .098 free bore which is perfect for mag fed 142g smks and puts the gas ring way into the case...i also have another 260 reamer that has .188 free bore which is perfect for 140g berger hybrids and 142g smks but wont shoot out of a mag as they are to long and again the gas ring is just inside the case maybe .030 or so.
not enough bullet in the case will cause the same issues as not enough neck tension...high ESs.
like i said the ideal length would be to do as i said above so that you can shoot different bullets from your mag...the hybrids and VLD bullets are going to be the longest as far as over all length and contacting the lands...youll see what i mean when you get your bergers and start playing with seating depths.
as far as seating depths and accuracy....ive found some where in between .015 to .035 off the lands has produced the most accurate loads for me...i dont like jamming or touching though i did it for awhile thinking that was the way to go but found i can load hotter with less stress on the case with a small jump...i dont shoot VLD bullets because the are sensitive to seating and i only shoot 2 brands of bullets...sierras and berger hybrids...if one of these wont produce a stupid accurate load something is wrong with the rifle.
just remember when building your dummy rounds...you need room to chase the lands as the throat burns out and you also need a little room in the mag...you need to balance these two things out.
I'm trying to find a picture of an SMK with a "gas ring" ????
im referring to the base and/or the starting point shank of the bullet ive heard ppl refer to both as a gas ring...i am assuming(my bad)that he was referring to the base...
http://www.mssblog.com/2016/06/10/bu...ets-1-diagram/
Longrange, pardon me if I am being slow. I believe I follow your math on how to reference the bullet lengths off of eachother. My question is once I determine the longest bullet that I will use for my dummy rounds, what length should I then load that bullet to? My understanding of the purpose of sending the dummy round in is to tell them where to set the lands in relation to the headspace. Within the length of my magazine there is a pretty wide variety of options.
Example: If I were to determine that a 175 SMK was the only bullet I was going to use in my gun and wanted to optimize performance for that bullet I still need to determine what length to set my dummy round to:
Overall Length Bearing Surface Seated into Case Shank Above/(Below) Case/ Shoulder Juncture Max SAMI - 308 WIN 2.8100* 0.2650 0.0380 Seated 1-caliber depth 2.7750 0.3000* 0.0030 Max Magazine
less 0.020" off lands
less 0.030" for erosion2.850* 0.2250 0.0750 Boat-tail / Bearing Surface even with Shoulder/Neck (no gas ring) 2.7720 0.3030 0.0000*
* = Fixed value to solve for
As I understand it, once I know what is "ideal" I would set my dummy round to the length listed above PLUS my buffer for starting point for seating depth from lands (0.020") and allowance for throat erosion over time (0.030"). This would put the lands in a position that my ultimate bullet length would be in accordance with the table above.
Thanks for your patience (you should see the spreadsheet I made to analyze this!)
ill post back later or in the morning with so examples for you.
i didnt have time last night to sit down and build some dummy rounds to use as examples so using just the numbers in your mag section you have posted above you have 2.850 as your max mag length..i would automatically change that number to 2.830 or so...if your primary goal is to feed from the mag you want some wiggle room there....next im not sure how the throat erodes in a 308 maybe some 308 owners can chime in on that...but id take another 0.050 or so off the 2.830 to chase the lands which gives you an COAL of 2.780.
if your building a single feed rifle then id seat the bullet to where i had 0.020 or so of the boat tail/shank junction past the neck/shoulder junction and that would give you room to chase the lands and still have good neck tension as the throat burns out.
as i said ive had the best luck with seating depth at 0.015 to 0.035 off the lands and most times have ended up 0.020 to 0.025 off....as far as some magic number there is none its what works in you rifle but just keep in mind you better off going a little short than you are going to long...i just built a mag fed rifle and had all sorts of feeding issues because my reamer had to much free bore...i tried a few different things and in the end i ended up buying another reamer and had two barrels rechambered...this was an expensive learning curve for me and why im telling you a little short is better than to long.
LongRange, thanks so much, this is exactly the information I was unsure of. The rest of clearly helpful as well in affirming that I was understanding what you were saying but I didn't have any concept as to how best to determine the seating depth.
Now I just need to wait for my shipment of Bergers to come in so I can load up some rounds and pick which I will be sending to Shilen.
Thanks so much for your patience and knowledge sharing.
and so we are clear by 0.020 past the neck/shoulder junction i mean the bullet seated deeper by 0.020 past.
Nice!
Berger hybrid or berger vld
Hybrids are about as sensitive to seating depth as a MK. Now I am not saying they won't shoot better when you find that magic spot. Just they are nothing like a VLD.
VLD's were designed to be shot jammed into the lands .001 to .002. Recently it was found that they would jump. If.interested read about how to get the greatest accuracy from your berger VLD. I know from experience it works.
If you are going to chamber a barrel especially for one bullet, if it is the VLD, how about a secant chamber. All chambers are designed around a tangent ogive. it would be a good experiment.
So I got my shipment of 168gr Hybrids so I could take some measurements. Based on discussions here, I will set my dummy round up to be seated 1-caliber length (.300) into the neck plus 0.020" to allow for erosion. At this length, the ogive of my bullet should be approximately 0.030" from the lands.
Based on these parameters I have the following choice to make:
- If I use 175 SMK as my dummy rounds (most commonly used) then the 168gr Hybrid will be seated approximately 0.100" deeper than ideal with an COAL of approximate 2.695" (0.116" shorter than SAMI max and 0.206" shorter than mag length)
- If I use 168 Hybrid as my dummy rounds then the 175 SMK will be seated approximately 0.100" shallower than ideal with an COAL of approximate 2.852" (0.042" longer than SAMI max and 0.049" shorter than mag length)
If I set for the 168 Hybrid then the 175 SMK would be seated with the bearing surface contacting 0.224" which may be reduced to 0.194" as the throat erodes. Seems to me like that might be getting seated a little shallow and maybe I am better off just living with the fact that if/when I use the 168 Hybrids they will be seated a little deep which would decrease case volume (i.e. increase pressure) and I may be giving up a little velocity. Thoughts?
Posting Permissions
Bookmarks