AA Lapua 123 Scenar ammo won't feed but Hornandy will?

[jurassic]

I have a BHW barrel that has no problem with Hornady Ammo, but jams the AA 123 grn Lapua scenar load into the feed ramp cuts on the extension. I tried 2 different magazines, did not make a difference. Hornady functions fine, AA ammo does not.

The Lapua ammo looks much longer, when measured from the ogive (caliper zeroed with the adapter in place) the Hornady is 1.6770, the Lapua is 1.7115, .0345 difference. Is this the problem? I don't have any other ammo to try at the moment.

The AA ammo measures 2.2670 OAL.

[jurassic]

Can anyone help me with this?

[tackdriver]

That is what aa scenars usually measure, do you have dies? If so just shorten them up a touch to same length as Hornady and gradually lengthen til you find to long then back up a step. If you don't have dies I have a few boxes of Hornady I would trade you.

[bwaites]

I have a BHW barrel that has no problem with Hornady Ammo, but jams the AA 123 grn Lapua scenar load into the feed ramp cuts on the extension. I tried 2 different magazines, did not make a difference. Hornady functions fine, AA ammo does not.

The Lapua ammo looks much longer, when measured from the ogive (caliper zeroed with the adapter in place) the Hornady is 1.6770, the Lapua is 1.7115, .0345 difference. Is this the problem? I don't have any other ammo to try at the moment.

The AA ammo measures 2.2670 OAL.

There aren't enough BHW owners here to make many guesses, so that's probably why you haven't had many responses. However, I suspect the problem is actually your mags, because that little bit of extra length shouldn't have a big impact. However, if the mag is presenting the cartridge at a little flatter angle than it should, the longer bullet might jam into the feed ramp before it has tilted up enough to chamber correctly.

Will the 123 Scenars single feed? (put an empty mag in, and single feed through the ejection port.) If you are doing this at home, take the firing pin out of your bolt, because you will need to repeat it multiple times and there is NO SENSE in risking an accidental discharge. You can do it safely at the range with the barrel pointed down range.

[LRRPF52]

What type of upper, what type of feed ramps, are the feed ramps blended to the upper?

[jurassic]

Thanks for the help guys. I did try 2 different types of magazines with the same result. The Scenar loads will not single feed either. Of course they can be single loaded into the chamber, fired, and eject just fine. The barrel and upper have m-4 feed ramps that appear to line up as well anything else I have assembled. I have a friend with a magazine made by AA, I'll try it next and also try the ammo in his gun. The fired cases on the Hornady ammo show two tiny bites on the the neck and the bottom part of the case so they must be hitting also. It may be the magazine not holding the round up high enough or the feed angle is wrong. I'll take some pictures.

The upper and lower are Aero Precision, the bolt is from LBC. What should the height of the mag be in relation to the receiver, maybe there is a problem. The receiver has not been used before. The upper worked fine with a different barrel. I can also try the upper on a Daniel Defense factory built rifle.

Is it possible the feed ramps are too narrow at the top? I was under the impression the bullet normally will not touch the ramps if everything is working correctly.

I'll give some of this stuff a try and give post an update.

[LRRPF52]

The sharp-nose HPBT's often get hung-up on badly-fit or blended uppers-to-M4 extensions, which is why I prefer to blend and polish them, while taking the edges off the barrel extension teeth that contact the projectile and case.

[jurassic]

Thats going to be the next thing I do. Will knocking off all the sharp edges on the front of the barrel extension cause any problems?

The sharp-nose HPBT's often get hung-up on badly-fit or blended uppers-to-M4 extensions, which is why I prefer to blend and polish them, while taking the edges off the barrel extension teeth that contact the projectile and case.

[LRRPF52]

The main concern is that the Barrel Extension is one of the most critical parts to containing pressure when the charge is ignited. As such, it is a strong steel that is heat-treated, with a surface hardness, and inner ductility.

The main areas on the barrel extension that bear stress are the threads where it is attached to the barrel, along the circumference of the part, and the inside teeth and substrate steel where the lugs of the bolt bear against it.

The question is, does polishing and lightly de-edging of the feed ramp side of the extension compromise the part's strength. I haven't seen anything to indicate that it does, but I would caution to remove as little as material as possible. I don't use any grinding tools, but just a soft polish wheel that is conical in shape, with a round nose. It has fine abrasive material embedded in a rubbery tool head.

I basically spend a lot of time placing the barrel back in the upper, comparing, then removing it and polishing some more.

[sneaky one]

Jurassic-I talked with L-52 while doing the -meltdown procedure this winter-, I was about ready to hone it too far, extra heavy duty buffing compound-he saved me from myself on this same procedure-less is more/ My new AR upper is sooo smooth, almost like a gunsmith did the work- = sweet.

[jurassic]

Thanks, I'll be headed to Home Depot to get some Dremel bits.

[LRRPF52]

I use the bits that came in my Ryobi tool. They are green, and feel like rubber.

Thanks, I'll be headed to Home Depot to get some Dremel bits.

These are the most dreaded words a gunsmith hears from his customer...after the fact. He he...

[jurassic]

I changed the ejector in the bolt, and now the gun feeds perfectly. I replaced my ejector with a new on that did not have any machining marks on it. I got the tip from the other thread about modding ejectors and figured I would give it a try.

http://www.65grendel.com/forum/showthread.php?6943-Ejector-Modification

[Nukes]

...The main areas on the barrel extension that bear stress are the threads where it is attached to the barrel, along the circumference of the part, and the inside teeth and substrate steel where the lugs of the bolt bear against it.....

Vaughn's Rifle Accuracy Facts was published 13 years ago and made the point that the first few turns of standard threads carry the stress. He also noted thread patterns that nearly equalized stress among all the threads of a joint.

What gunsmith and barrel maker has not read of the stress distribution, but who has altered thread patterns accordingly? Anyone?