I just completed my AR15, and brought it to the range for a function test. The results were a little disappointing.

My bolt will close over a "go" gauge, but not over          
a "no-go" gauge.

When I got to the range, I pulled out the three boxes of ammo I expected to shoot. They were:
a box of Federal 55 gr ( with Lake City headstamp ), a box of PMC 55 gr FMJ, and a box of Winchester
62gr FMJ. First, I tried the Federal. I could not get the bolt to close over the round. Several minutes and much cussing later, I got the live round out. Same experience for next two rounds of Federal, after which I gave up and switched to PMC. Same thing. I switched to the Winchester 62gr stuff, and everything worked fine. No problems whatsoever. Not even a little tight.

Is this normal? Did I choose the wrong ammo?

Anyway, I guess you guys need some details about my hardware. I'm not sure what's pertinent, so I'll try to be fairly complete. I have an Olympic Stainless Ultra Match bull barrel w/ 1/8" twist ( 20 inch barrel ). My upper receiver is a DPMS A3 flattop upper. My bolt/bolt carrier assembly is a Les Baer.

Sam

You have a SUM barrel, Read Match reamed 223 barrel.  This chamber is set up tight, real tight.  This allows you to reload for the barrel to produce some outstanding loads/accuracy.

If your planning on shooting 5.56 Nato loads, you have the wrong barrel, and will need to replace the barrel with a Nato reamed one.  

Note: Please do not destroy this barrel by opening up the chamber and reaming to Nato specs.  This barrel is breach cut, and tightly reamed to achieve match accuracy with match ammo. If you feel that you need to fire Nato ammo, buy a new barrel and sell the barrel to someone looking for a Match barrel that plans on running match ammo threw it.

I realize that this is a "minimum saami spec chamber" in a match barrel. I didn't expect that
off the shelf PMC would jam me up tight. What inexpensive ammo can I use to continue my break in procedure? I don't want to waste my Federal Gold Medal match ammo on the break in when my scope hasn't come in, yet. I knew the Federal stuff was iffy... Can I shoot the bulk Winchester 45gr stuff?

I have no intention of getting anywhere near this barrel with a reamer. I just wanted to make sure this wasn't some weird headspace problem. I can deal with having to be picky about my ammo.

Sam

Run Black Hills ammo. Hell, you may even find one of their loads that may group better in the barrel than the Fed Gold.  But, you will find that your own secret formula hand loads will hands down, group the best. As for the 45gr ammo, the barrel spin is a little fast for it, but may work in the mean time (might have to seat the bullet a little deeper in the case to allow loading).

When cleaning the bore, Use Sweets to clean it.  On broach cut rifling, the cutting tool will leave Micro burs as it cuts, and standard bore cleaning (read slow reaction cleaners) will not get the copper fouling out of the cuts without scrubbing.  

On broach cut barrel, I will very seldom run a brass brush down the barrel. Instead, I use a nylon blush with Sweet's bore cleaning to dissolve the copper fouling, then follow the brush with a patch soaked in Sweet's to finish off any fouling that may still be left.  Just remember to get all the Sweet’s out of the bore, then run a Oiled patch down the bore to prevent rusting (yes, even on SS).

During break in, just run a patch lightly soaked in Sweets for a few passes down the bore, then run a few dry patches (run the bore dry during break in).  This will allow the fire bullet to uniform the lands and grooves, and polish out the micro cutting burs left by the broaching tool (will just even the tops of the burs).

P.S. On your chamber, the throat is cut short.  This allows the use of heavery bullets where the octive of the bullet is longer, and allows the heaver/longer bullet to be seated in the case to fit into the mag, and still be very close to the lands of the rifling when loaded into the chamber. The problem that you are running into is that some of the bullet tips are short (short octive with the diameter of the bullet at the front surface being larger than a longer octive bullet), and the lighter bullet is engaging the lands at loading, causing what apears to be a short chamber.  Your head space is correct, it's the bullet tip that is wrong for the cut throat.

Ah. Very helpful, thanks *VERY* much! I'm looking
forward to seeing some very small groups at 300 yards. I've just heard that it will probably be
mid-January before my scope comes in. *sigh*

Until I'm ready to place an online order, I guess
I'll keep using the Winchester 62gr FMJ's. I honestly never thought about the shape of the ogive. I have the dies, primers, powder, and
bullets on hand, but I haven't bought any brass, yet. I was thinking about getting 100 Lapua cases.
I didn't think it was worth the effort to get too
worked up when my scope still hasn't made an appearance. Thanks again for the info.

Sam

Lapua has great brass, but you are under thinking the amount that you will need.

Since the rifle is an autoloader, think in the 1000 lot for a brass buy.  By the time that you prep the brass (turning necks, unifying primer holes, trimming, then weighting out the brass into groups), you will find that you may end up with three to four different brass groups.  My advice is to just pick up a thousand lot of USA made brass, then re-clean and get to work.  This way, you can have several hundred rounds of loaded ammo that are the same (loaded at the same time, instead of taking the chances of something changing before you reload the next group).  

Once you have found the correct bullet tip and seating depth, powder and weight and the weather/temperature doesn't change, you will be set.  The only problem that I run into is once I find a great load, the season’s change and that load goes to shit.  Nothing like having a .3 pet load in a bench rifle go plus .7 just because the temperature went up by 40 degrees.  On the AR's, if I find a load the stays around 1MOA without the temperature affecting the load, I will just run that load.  The bitch is that Gun powder lots change all the time, so when you buy that single pound can to test loads, once you find the magic load, you have to find 8LB kegs of the same lot to hold you off for the season.

Welcome to searching for the "Holy Grail". Just when you think that you have reach your goal of the perfect load, the barrel goes south, and you end up starting from scratch.  On your sum barrel, the groups will tighten up for the first hundred rounds then hold for around 3000/5000 rounds, then start to open back up.  Not running a brass brush threw the barrel will extend the rifling life (compensate for the throat plasma erosion by seating the bullet out a little longer), but it will go south sooner of later. A great barrel gets you so far, then great hand loads gets you a little father Lowering the MOA on the groups, but it all comes down to if the “*Nut” behind the trigger is doing his part.

*Nut = anyone that spends way too much time at the loading bench, and thinks in the thousands of inch when seating bullet in a case.  The part that puts you over the top is when you re-mic/weigh the ammo after you are done, and then pulls the separated ammo down if it mic’s .002/weighs 1 grain off the held control