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marks655

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Barrel life question:

I have an 'prarie dog' AR-15 built by Bill Wylde - has a 24" Krieger stainless barrel. I've put about 2,200 rds thru it. All handloards, mostly 55 gr Sierra Gamekings, 26 gr W748.

Doesn't group as tight as it did for the first 1,200 or so rds. I clean it every 20 rds when shooting paper and I never clean it during a dog-day. Bore looks good, doesn't foul and still has nice crown.

Could this be a barrel 'throat' thing ?
 
Maybe, but that stainless barrel should give you around 3500 rounds. A shot-out barrel generally shows up by presenting occasional fliers that become more and more frequent over several hundred rounds. General widening of the goups isn't usually the sign.

The barrel is at the age where you can see some heat stress cracking in the throat area. You could try David Tubb's Final Finish to clean it up. I would also get a Stoney Point seating depth gauge and see how far forward you can seat your bullets? Cut your load a little and start about .005" off the lands, and try backing the bullets up in .005" increments to see if you can find a seating depth sweet spot? If so, see if they'll still feed OK?

Also, I would check what else has changed? Brass brand, for example, or even the lot of brass? When I shot ball powder (AA 2520) in my M1A I found it cut my groups 40% to debur the flashholes in the cases. It made no difference with stick powders, but ball powders are harder to light. Some cases have better formed flashholes than others, and that's why this difference popped into my mind.

Try getting a handful of Norma cases (buy a box to shoot). These are much more consistent than others I've measured. Dedicate them as your accuracy check cases. Work up the 748 load in them and see how the gun groups. You can repeat that experiment in 1000 rounds and see whether the groups are changing?

Good luck,
Nick
 
Should I expect better ?

The rifle is a modified Colt AR-15 and the magazine size limits OAL to about
.040 " off the lands for most loads. I have 100 pieces of Norma brass I use to load various 'check loads' but I can't seem to get a particular load to really stand out. All have some flyers, and most shoot nice <.5 MOA 5-shot groups sometimes but I can't seem to get a consitent string of good groups. I also tried turning the necks but that didn't seem to make any difference. I always de-burr the cases and I seat the bullets using a Redding 'benchrest' style seating dye with a micrometer-type adjuster. Sometimes I wonder if the process of chambering rounds in a semi-automatic rifle has an effect.

Even when just broken-in this rifle would shoot one 0.4" group, then 0.8", then one at 0.6 and another back to 0.4 and then one with a flyer opening the group to over 1 inch, etc. - never 'consistent small groups. ' I get the
1st three shots in under 0.25" sometimes. When shooting groups I clean every 20 rds and try to keep the barrel temp no greater than 'warm.' The barrel is a Krieger 24" and chambered and installed by B. Wylde with a fiberglass 'sleeve forestock.' The upper has been modified by Wylde - handle cut-off and a custom weaver-type base; custom stainless gas block; JP trigger.

I shoot from a Wichita benchrest and a leather bag. Maybe this is as good as it gets. Should I expect better ?
 
I see a small advantage with extruded powder in my Krieger-AR, Re 15 or Varget. But I sure like the way Ball meters and will probably try some AA2520 again to see if I can dial it in.

There are magazine modifcations that take longer OAL. I think it turns the magazine into a single stack. I'd shoot some strings single shot with the bullets loaded closer to the lands and see if that might be worth the trouble.
 
I've ran into a very simmilar problem. I have a DPMS 24" special. I have shot about 2000 rounds through the barrel, about 90% handloads. My groups have also gone sour. After reading this post and someone mentioned brass, i thought of something. I don't think i have thrown out more than 50 peices of brass over the last 2-3 years of shooting it. I bought it as new winchester brass from midway. Could the brass be worn out?
 
longer barrel life possible ?

Thanks for the feedback. I cleaned-up the crown and polished the throat with the pink JB stuff. Will post if it improves. If not, probably send the upper to Krieger to fit a replacement tube.

Any ideas on how to extend barrel life ? This is only an issue for me with the AR-15's. I have shot as much as 500 rds. in a weekend (after Nutrea). Maybe I should get a .17 for Nutrea.

I had thought SS would tend to be longer life than CS. I also tend to think chrome-lined tubes live almost forever. Does anyone make a highly accurate chrome-lined tube ?:confused:
 
Usually a SS barrel should shoot around 3500 rounds. Chrome-moly runs around 3000. You can gain about 20% (go to almost 4000 rounds) in SS by having it cryo treated (and I believe John Kreiger is cryo treating his barrels). I have seen claims that Chrome-moly responds more dramatically to cryo treating than SS and will have its life extended even more, but Mete says there isn't solid literature to support this. Worth a try, in my view.

It bothers me that you get good groups sometimes and not others. Three more things to mess with:

First, you are correct that self-loading can affect a cartridge. If you have a concentricity gage, measure the runnout on a half a dozen bullets right out of the Redding seating die. You will find they are very good. Next time you are at the range, load the magazine and shoot, manually ejecting and catching every other live round in your hand. When you get home, measure the runnout on the ejected rounds. If it is like my M1A, you will find a number of the bullets have been tipped in their case necks significantly.

Also, while you are shooting, fire some single-loaded groups for comparison. In service rifle matches the 600 yard slow fire phase is always singly loaded and that is the only way it is safe to use the thinner turned necks. Try going through finding a seating depth sweet spot as I described, just for single loading.

Second, years ago pistol competitors noticed that military match ammo would outshoot commercial match made by the same company using the same components. It turned out to be due to the pitch used to seal the bullets in the case. It sticks just enough to increase the start pressure and makes that start pressure more consistent. This leads to a couple of things you can do about start pressure: get a Redding sizing die with the interchangeable neck bushings so you can try a tighter neck; get a Lee factory crimp die and see how it does with your bullets? You need to concern yourself with the age of the brass because it gets more springy as it work hardens with age, tending not to neck down quite as far as it did originally. Neck annealing can fix this, but you see a lot of arguments about the effectiveness of home annealing methods and tools.

A third possibility is that you are getting a secondary pressure spike. These can be dramatic and inconsistent, and the .223 has been known to get them, even with some factory ammo. This phenomenon occurs mainly with the light, fast bullets propelled by slow double-base powders. Charlie Sisk has actually blown up a number of barrel muzzles with secondary pressure spikes and without any pressure signs appearing on the case. It seems to be a high brissance detonation near the base of the bullet as it's about to exit the muzzlem and only seems to occur starting at nearly 20" down a barrel. If you were getting this problem, it might well be inconsistent and cause fliers. The cure is either to move to heavier bullets or go to a faster single-base stick powder. To learn more about it, read this and this.

Nick
 
Unclenick:

Thanks for the reply. I use mostly ball powders - W748 powder or AA2230. I have loaded some Hodgdon Benchmark powder to try - it is a short extruded type, I think.

One question: you mentioned 'single fire' with a semi-auto. Do you mean simply placing the round on top of the magazine? or in the chamber ? I would tend to think it would be hard on the extractor to feed rounds in this way. What is the proper way to load 'single fire' ?

I agree with you about bullet seating. I tend to load into the lands on my bolt guns to avoid inconsistent initial pressure curves when the bullet begins to move. It doesn't give tighter groups, but it does give much more consistent results. This is, of coarse, impossible with an AR-15 because there is no 'camming action,' per se, to push the bullet into the lands.

I will try loading as close as possible to the lands and loaing 'single fire.'

I know the AR-15 can beat-up bullets when feeding. I noticed it deformed the soft lead nose of sierra spitzers and I switched to HPBT.

I'm not displeased with the rifle per se, since I use it mostly for varmits, and it does very well. But I would like to get better consistency.

One more thing: The forearm tube has some holes drilled in it for ventilation - top and bottom. Should I cover the bottom ones so they won't 'grab' my shooting rest bag ? Could something as simple as this cause fliers ?

Thanks.
 
Fliers can just be a bear to trouble-shoot. Try placing a lubricating sheet of heavy polyethylene between the bag and the gun if you think grabbing is a problem, but I doubt it is the main thing.

Most of the companies catering to match shooters, like Sinclair, OK Weber, Champion Shooter's Supply, or Champion's Choice will all carry what are called single-loading magazine "sleds", or even special single-loading magazines. Single-loading sleds are magazine follower substitutes that give you a platform so you can place a single round on them through the ejection port without puting it in a magazine. They have a shallow channel that keeps the round lined up with the chamber rather than being left or right of center, so it doesn't tend to hit the divided feed ramp and move the bullet on its way in. These are what most shooters of detachable magazine guns use.

You can set the rounds directly in the chamber. Just don't get burned by hot metal if you are shooting fast. The military auto extractors pop into place without any problem.

The business of starting on the lands and backing out is because some guns don't shoot their tightest touching the lands while some do. You'll have to find out for yourself.

I got the newest issue of Precision Shooting in the mail today. M.L. McPherson has an article in which he mentions one cause of irregular fliers from loads of powder that nearly fill the avalable case capacity. If the bullet is long enough so it seats with its base protruding down into the powder, sometimes the bullets push the powder aside and sometimes the powder refuses to get out of the way and becomes compressed. These compressed and uncompressed rounds will shoot two distinct groups. The lesson would be either to choose a powder that doesn't come up any higher than the base of a seated bullet in the case, or one which is always compressed by the same amount (all the way to the top of the shoulder, for example). I don't know what your loads are, so I don't have any idea whether this might apply to your bullet an powder combinations or not?

Nick
 
Unclenick:

I may load some just-off the lands and try placing rounds part-way into the chamber. I have about 100 pieces of de-burred Norma brass that has been used only in this rifle, but I have not sorted them by weight. Is that something I should do - even with the Norma brass ? I tried turning necks with some weight-sorted cases and saw no difference - but that may be because of bullet seating/distortion from autoloading, etc.

My handloads for the AR-15 are always moderate or light. Mostly 55 gr Sierra HPBT Gameking bullets and 26-26.5 gr W748 which does not come even close to the case neck. Heavier bullets (e.g. 69 gr match) don't seem to give any better groups than the 55 gr.

I had hoped to get consistent tight groups from the magazine as is described in the book 'Black Magic' - by John Feamster. Feamster authored several articles in Precision Shooting some years ago, one of which inspired me to get Bill Wylde to build a 'varmit' AR-15 for me some years ago. The rifle has never shot consistent strings of small groups, but the 'average' group size (roughly 0.7 MOA) and the exceptionally small groups it does shoot some of the time (< 0.3 MOA) has kept my interest. I would be happy with an average group size around 0.5 MOA from the magazine. As for varmiting, well, it has never really been tested. I have used it mostly on Nutrea in Alabama which doesn't require high precision because of range and target size. I hope to get to Nebraska this spring and use it on prarie dogs.

Thanks for your advice.

MSS
 
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