AR15 chambering problem??

[Doc Holiday13]

So yesterday I shot my first service rifle comp. It was a fixed yardage at 200. It was a "fun" shoot according to the match director so I was allowed to use my rifle. Its a 10.5" barrel bushmaster barreled flattop upper with removeable front and rear sights(not exactly what we call a competition gun, but its my first match ever) Don't criticize the gear, just help me fix the problem.

During the match temps never got above 30 degree's and we had wind gust up to 20mph.

First mistake(maybe) was that I shot 60 rounds through the gun 2 weeks ago and never cleaned it. But I've run the gun a lot dirtier and harder than I did for this match and NEVER had a problem. For the match I used all handloads.
Round 1: 20 shot 2 sighters Slow fire.
Didn't have a single problem with anything I fired really well and scored a 151
Round 2:Rapid fire sitting 10 shots 2 sighters
First round went BOOM...second round click... Yank charge handle drop another round into chamber, BOOM!. Next round click...
All in all I got 4 shots off due to the rounds not going off

I specifically loaded all these rounds for this match and I double checked primer seatings. Some primers had the smallest of primer strikes(almost not noticeable) some didn't have any primer strikes!!!
Round 3: 10 shots rapid fire prone 2 sighters (simulated 300 yard targets)
same problem as above except I got 3 shots off

Round 4: 10 shots slow fire 2 sighters (simulated 600 yard targets)
A few rounds failed to go boom(i pulled some factory loaded ammo out of my bag at this point) and I was so frustrated at this point I lost my head and lost count of my rounds so I failed to shoot all 10 rounds.

Final score of 233 with a failure to shoot 15 shots

So what could be the problem here? Like I stated already I've run the gun much dirtier than I did without problems, but never in such cold temps. I'm pretty sure I have a standard hammer springs. The only thing I can come up with is that my buffer spring is cheap and it was so cold it caused it to shrink and loose some of its springy-ness. That and a slightly dirty chamber

 

[wnroscoe]

Re: AR15 chambering problem??

Remove the carrier and bolt from the upper. Dissasemble the bolt (firing pin & spring) and clean thouroughly with Brake Parts Cleaner, inside and out. Clean the inside of the carrier with same and try to remove carbon if present. If the rifle is cycling enough to throw out an empty the bolt carrier assembly should be cycling far enough back to drive the neck round home and fire. If you've been running it wet the oil may have started to gum up a bit in colder temps with powder / carbon residue.

When firing the last round in the magazine did the bolt carrier lock to the rear?

If all looks good, I'd suspect the spring like you mentioned.

 

[jarheadkp]

Re: AR15 chambering problem??

Doc,

What are the components are you using? Also, since you are shooting a shorty, it's most likely because you didn't clean the rifle. The gas tube has been shorten to accommodate for the barrel length. Carbon will build up in the bolt more quickly than the standard length. If you are using ball powder, it tend to foul more than extruded powder. Clean the rifle and go back to the range to see if it will function.

 

[762-4-U]

Re: AR15 chambering problem??

Clean it....sounds like the carrier was not going all the way forward to allow the hammer to fully strike the firing pin.

Oh and +1 on the brake cleaner. its gun cleaner at half the price.

 

[Doc Holiday13]

Re: AR15 chambering problem??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">Remove the carrier and bolt from the upper. Dissasemble the bolt (firing pin & spring) and clean thouroughly with Brake Parts Cleaner, inside and out. Clean the inside of the carrier with same and try to remove carbon if present. If the rifle is cycling enough to throw out an empty the bolt carrier assembly should be cycling far enough back to drive the neck round home and fire. If you've been running it wet the oil may have started to gum up a bit in colder temps with powder / carbon residue.

When firing the last round in the magazine did the bolt carrier lock to the rear?

If all looks good, I'd suspect the spring like you mentioned. </div></div>

I do use a really heavy oil. Mobil1 15w-40 to be exact. The oil doesn't burn off and it makes cleaning the gun really easy. BUT I did notice went I pulled the bolt the other night that the oil was almost pasty because it was sooo cold. I already use brake cleaner and I chamber brushed it out followed up with a oiled swap last night

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: McCarthy</div><div class="ubbcode-body">Doc,

What are the components are you using? Also, since you are shooting a shorty, it's most likely because you didn't clean the rifle. The gas tube has been shorten to accommodate for the barrel length. Carbon will build up in the bolt more quickly than the standard length. If you are using ball powder, it tend to foul more than extruded powder. Clean the rifle and go back to the range to see if it will function. </div></div>

I just switched to ball powder and was noticing the bolt turning black during the match(I have a fully blasted and polished carrier).

All is clean now and i can chamber rounds slow feed with the forward assist. I don't know if they fire, but they chamber nicely and are easy to extract via charge handle . So it may have been a culmination of my lubrication of choice, cold weather, and new powder type. I'm gunna have to take the gun out and flog it, let it cool, and try to flog it again before it gets warm

 

[USMCj]

Re: AR15 chambering problem??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DocHoliday13</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">Remove the carrier and bolt from the upper. Dissasemble the bolt (firing pin & spring) and clean thouroughly with Brake Parts Cleaner, inside and out. Clean the inside of the carrier with same and try to remove carbon if present. If the rifle is cycling enough to throw out an empty the bolt carrier assembly should be cycling far enough back to drive the neck round home and fire. If you've been running it wet the oil may have started to gum up a bit in colder temps with powder / carbon residue.

When firing the last round in the magazine did the bolt carrier lock to the rear?

If all looks good, I'd suspect the spring like you mentioned. </div></div>

<span style="font-weight: bold"><span style="font-size: 17pt">I do use a really heavy oil.</span></span> Mobil1 15w-40 to be exact. The oil doesn't burn off and it makes cleaning the gun really easy. BUT I did notice went I pulled the bolt the other night that the oil was almost pasty because it was sooo cold. I already use brake cleaner and I chamber brushed it out followed up with a oiled swap last night

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: McCarthy</div><div class="ubbcode-body">Doc,

What are the components are you using? Also, since you are shooting a shorty, it's most likely because you didn't clean the rifle. The gas tube has been shorten to accommodate for the barrel length. Carbon will build up in the bolt more quickly than the standard length. If you are using ball powder, it tend to foul more than extruded powder. Clean the rifle and go back to the range to see if it will function. </div></div>

I just switched to ball powder and was noticing the bolt turning black during the match(I have a fully blasted and polished carrier).

All is clean now and i can chamber rounds slow feed with the forward assist. I don't know if they fire, but they chamber nicely and are easy to extract via charge handle . So it may have been a culmination of my lubrication of choice, cold weather, and new powder type. I'm gunna have to take the gun out and flog it, let it cool, and try to flog it again before it gets warm </div></div>

DING DING DING DING DING!!!!! we have a winner!!!!

Use either CLP or Birchwood Casey barricade (almost the same thing as CLP) Motor oil is way to thick!!!

 

[Doc Holiday13]

Re: AR15 chambering problem??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USMCj</div><div class="ubbcode-body">
DING DING DING DING DING!!!!! we have a winner!!!!

Use either CLP or Birchwood Casey barricade (almost the same thing as CLP) Motor oil is way to thick!!! </div></div>

Yeah that would involve me going out of my way to buy a "special" lube. I have several gallons of motor oil in my garage. This is the only time its ever failed me. It doesn't burn off it makes cleaning a cinch cuz it grabs all the carbon. I just pull out the bolt wipe everything down and re-apply. I think I'll switch to 0w-40 for cold weather like I did with my pickup

 

[jarheadkp]

Re: AR15 chambering problem??

Make sure you check the dip stick before you fire the first round and change the oil after 3000 rounds!!! Where's the oil filter on that shorty???