450 Bushmaster Bolt Extractor/Ejector function test.

[AR_Hunter]

I'm using factory Hornady 450 ammo.

[Hoot]

I'm at work, so I can't A/B it to mine, but one thing I did do to my extractor before I put the first shot down the barrel, was to polish the leading edge of that hook so that it slides over the rim with the least resistance as possible as it picks up a round. Many will polish themselves over time. If you ease a round into the chamber, when the bolt stops traveling, usually short of battery, can you easily thumb it into battery with the forward assist? If you can, chances are it's not a problem engaging, but one that occurs during extraction. If it were mine, I'd take the bolt out of the carrier, squeeze the extractor into it with my thumb while pressing out the retainer pin with a punch, withdrawal the punch and ease off on the thumb. Then set it sown on a surface and allow the extractor to fall free from the bolt as it should. Using magnification, examine the inside of the extractor and the well it rests in for any foriegn particles, parkerizing buildup, etc. Also examine the spring and if it has one, the rubber booster. Looking for something that would not allow it to easily over the case rim as it picks up a cartridge.

If everything looks ok, give it a drop or two of lube and put it back together. Now, take a live case and hooking the extractor with it's rim, pivot the case until it's depressing the ejector plunger and it is sitting flat against the bolt face. It will require some force and steady hands due to the ejector spring. Did it go all the way in flat without feeling odd? Here's the tricky part. While holding it in contact with the bolt face as if it were locked in battery, feel the height of the extractor body as compared to the rest of the bolt body in the area of the scrapes. Does the extractor sit higher than the rest of the bolt's surfaces in the same area? If it does, that would account for it dragging against the lugs and effacing the finish. It would also indicate the problem is in the bolt or extractor manufacturing dimensions as opposed to the barrel extension. Is this making sense?

While you have the BCA out, separate the upper from the lower and secure the upper in something that can hold it bore down and free up your hands. With a flashlight and magnifying glass, look at the barrel extension lugs in the vicinity where the extractor passes going into battery. Do you see any foreign particles? Do you see any scratches that you can not account for or that look obviously different than the wear on the other lugs? There's got to be a surface somewhere in the barrel extension where that extractor is rubbing against.

If nothing jumps out at you, put the two halves back together but leave them levered so that the breech of the upper is above the lower, say in a cleaning fixture and preferably with one of those delrin and steel pin cleaning gizmos locked into place. IE like you're going to clean the barrel. Wipe the extractor clean in the area of the scrape and using a q-tip moistened with a little alcohol, acetone, brake cleaner, etc (not dripping), degrease the wear spots and then blacken them with a sharpie or marks-a-lot. Reinstall the bolt in the carrier and place the charging handle and carrier back in the upper. With no cartridge in the gun, using your your thumb, gently push the carrier into battery and pull it back out with the charging handle. Repeat several times. Does it feel unduly resistive to motion either way? there's always a little resistance if you have not worn it in good. Pull the carrier back out and examine the extractor. is the sharpie worn off? If so, can you see where in the upper it wore off on? If not, repeat with a cartridge. Make the same observations. If none of that causes the sharpie to efface, then you can assume it is a post firing event.

I'm betting you'll see it scraping without having to fire it. I'm also betting the problem is in the bolt body or ejector dimensions. At some point, you will identify the culprit. At that point, you will need to decide whether to contact Bushmaster to see how much of the upper you're going to have to send in for warranty repair, or whether you want to just correct it yourself once you determine what's causing it to rub. BTW, was all or most of the ammo fired through it so far, from the same lot? Have you inspected the dimensions of a few of the spent case rims and extraction grooves to determine that you didn't get a lot of ammo with poor case dimensions? There actually could have just been a few bad cases, but enough to cause the scratches. In that case, you should inspect all your brass if you intend to reload it, to separate out any cases that are out of tolerance.

Hoot

[lungingturtle2]

AR Hunter, it appears that the circular grooves in back of the bolt locking lugs (on the bolt and the extractor) do not line up and are 0.030 - 0.035" out of alignment, this is enough to prevent the extractor from slipping over the case rim. I checked mine and they line up exactly. Call Bushmaster and talk a Q.C. tech to see if this has ever been an issue. Also if you know someone who has a .450B change bolts and see if his extracts in your upper. Hope this helps. Mike in Illinois.

[wildcatter]

Here's the best pictures that I could manage to take. Please let me know if this is the same wear characteristic that you see on your extractor. I compared it to my .223 and after several thousand rounds it looks nowhere close to the wear that the 450 one has at 15 rounds.

[ [url=http://farm8.staticflickr.com/7151/6644540013_12eed37dd8_z.jpg] ][/url]
Extractor Lug Contact by patrick-collins, on Flickr

[ [url=http://farm8.staticflickr.com/7006/6644539135_434ca623fb_z.jpg] ][/url]
Extractor Lug Contact by patrick-collins, on Flickr

I see it now, my learned guess, is that you are indeed having a problem, with the extractor, coming into contact with the the Male locking lugs of the barrel extension, from either an out of spec extractor or barrel extension, or both, in production anything can happen. They test fire for this at the Factory, but if the test ammo has a groove that is at the bottom of the spec, and the your fifteen rounds are also, then this can happen.

You're going to need to really clean (as in scrape with a sharp knife, you're looking for carbon build-up) the underside is the extractor and the bolt groove it sets in. If this persist, then you're going to have to reduce the two offending lugs somewhat and this is best done by a professional, or better yet, send it back just like it is and include the pictures and an explanation of what you think the problem is, based on my observation. This is not such a bad idea, because you'll have a real GunCrank, looking over and tuning up your entire system, as opposed to a trained Production Person, who assembles parts.

..t

[Texas Sheepdawg]

I took a bunch of pics and posted them on Photobucket in this album.
http://s105.photobucket.com/albums/m229 ... ushmaster/

[Hoot]

AR Hunter, it appears that the circular grooves in back of the bolt locking lugs (on the bolt and the extractor) do not line up and are 0.030 - 0.035" out of alignment, this is enough to prevent the extractor from slipping over the case rim. I checked mine and they line up exactly. Call Bushmaster and talk a Q.C. tech to see if this has ever been an issue. Also if you know someone who has a .450B change bolts and see if his extracts in your upper. Hope this helps. Mike in Illinois.

Looking at dawg's bolt, his grooves do not line up either, so there many not be a tie in to that. My bolt is at a gunsmith in Texas for headspacing a chamber right now, so I can't offer much assistance. I do have a brand new spare extractor you can borrow if you want.

Hoot

[Texas Sheepdawg]

AR Hunter, it appears that the circular grooves in back of the bolt locking lugs (on the bolt and the extractor) do not line up and are 0.030 - 0.035" out of alignment, this is enough to prevent the extractor from slipping over the case rim. I checked mine and they line up exactly. Call Bushmaster and talk a Q.C. tech to see if this has ever been an issue. Also if you know someone who has a .450B change bolts and see if his extracts in your upper. Hope this helps. Mike in Illinois.

Looking at dawg's bolt, his grooves do not line up either, so there many not be a tie in to that. My bolt is at a gunsmith in Texas for headspacing a chamber right now, so I can't offer much assistance. I do have a brand new spare extractor you can borrow if you want.

Hoot

Is this what you mean?

[swiftdriver]

Ar hunter, When you fired the 15 rounds, did the rifle eject the empty's? If so I think you really need to look at the head space. Remember the extractor can hold the cartridge against the bolt letting the rifle fire and then eject. After the ejection the next round may be pushed ahead of the extractor too deep into the chamber for the firing pin to hit it if the head space is way off. I can not find this bit of info in your previous posts thanks. Kirk

[AR_Hunter]

Here goes...

After reading Hoot's novel (awesome at that) I'd already done most of the checks described. I gently filed down some of the metal in the areas that were rubbing upon entry into the barrel extension lugs. The action was much smoother but I still had the same problem of not being able to extract the round from the chamber. I did pay close attention to the actual extractor rim as well as the extension lugs. All is well there. After rereading lungingturtle2's comment about the groves not lining up, I realized my extractor is not even close to being long enough to reach the top of the rest of the bolt face/lugs. I measured it and it is .017 inches short. That got me thinking... You can put a shell/round under the extractor and it will hold it firmly against the bolt face but it is pretty hard to do. In theory it should be a little longer allowing a tad bit more room. So...I put an empty shell into the chamber, slammed the action home and then put a cleaning rod into the muzzle until it was inside of the empty shell. I pushed like hell and sure enough you could faintly hear the extractor click. Mind you, the shell BARELY moved but it did hook underneath the extractor. I held my breath and pulled the charging handle and the case shot out across the table. I'd like to try Hoot's extractor as I think that will solve the problem. The case didn't move near enough for me to think it's a headspace problem but if the extractor doesn't fix it I'll have to send it in to Bushmaster. At the present place the extractor is making contact, I'm not suprised that some of the extractors on this forum have been broken.

To answer a few of the other questions:

I'm checking the gun using two different lots of Hornady ammo and they both have the same dimensions.

While shooting the gun it ejected the rounds sometimes but I did have to push out one case using a cleaning rod. That was one of the last shots I took. The gun always fired with each pull of the trigger.

Thank you all for your suggestions and posting pictures. I'm sending Hoot a PM and will post any new info when I have something else to share.

[wildcatter]

I don't think I made myself clear enough. Those shiny spots, on either side of the lug, on the back of the extractor are from the Barrel extension lugs. This is cause by the extractor being held outboard by the rim. Try this, Remove the Upper, dissemble the bolt, only removing the "Ejector", reassemble the bolt carrier group, slide the case under the extractor, which is still in the bolt then slowly slide the bolt and carrier group forward in the dissembled upper and see if the lugs lock. This should happen with zero effort. You'll know when you're home when the carrier is flush with the back of the upper. If the extractor is held up by the extension lugs, the carrier will be say 3/16th inch from flush, but noticablt not flush, because you checked for this "Flushness" (if that's even a word, I hope you know what I mean), before you did any of this, so that you'll have a reference, for comparison.

Please check this and get back, I want to know where the carrier is in relation, to the back of the upper, is it flush or what??..

..t