Photo request: extractor issues with new .450BM build

[Muad]

Hello, new to the forum, and the .450BM. I just put together my first .450BM upper, using all Franklin Armory parts minus the upper receiver and bolt carrier (those are both Colt).

After opening up the ejection port opening on my upper receiver to accommodate the .450BM case, I noticed that the bolt would not go into battery, which appears to be due to the extractor not wanting to slip over the case rim. No matter how hard I "sling shot" the charging handle, it will not slip over the case rim. Pushing the forward assist helped nothing.

So, I was hoping some of you fine folks could take a close-up photo of your .450BM bolt face (with the extractor installed) so I can compare them to mine? The only way we could get the upper to hand cycle properly (feeding and extracting/ejecting like it should) was to shim the extractor about ~.030". To us, it looked as though the extractor claw was too far inside the bolt face circle (if that makes sense), so the extractor was just pushing against the bottom of the case rim, rather than pushing and slipping over it. Shimming the extractor out allowed it to slip over the case rim, and still extract the case fine by hand, cycling the rifle using the charging handle (with the firing pin removed for safety).

I'm trying to determine if I have an out or spec bolt, extractor, etc. BTW, after reading a long post from Hoot, I measured the cases on my new Hornady Black ammo, and they are measure about .470" and .400" (versus .473" and .409").

Any help is greatly appreciated!

Blessings,

[Muad]

Here are some photos of the bolt face to show you the extractor's position. Note that we also added a radius to the front lip of the extractor while playing with this early this morning. The radius that was on there was almost non existent. Adding that made no difference on function prior to shimming the extractor.

No shim installed (will not slip over the rim case and go fully into battery):

Shim installed (seems to operate perfectly when hand cycling):


If one were to order spare extractors, would 7.62x39 or .458 extractors work? I can't seems to find them for .450BM.

[Pig_Popper]

Are you attempting to use a 5.56 bolt <Colt> ?

If not, what caliber bolt is it and can you provide the bolt face depth and inner diameter measurements from your Colt bolt.

Based on the top photo id pop out the cross pin and inspect the extractor spring and replace with a new one to rule that out as a cause for concern . while you're in there it wouldn't hurt to take the sharp edges off the ejector from 3 to 9 o'clock a slight bevel...

[Muad]

Are you attempting to use a 5.56 bolt <Colt> ?

If not, what caliber bolt is it and can you provide the bolt face depth and inner diameter measurements from your Colt bolt.

Based on the top photo id pop out the cross pin and inspect the extractor spring and replace with a new one to rule that out as a cause for concern . while you're in there it wouldn't hurt to take the sharp edges off the ejector from 3 to 9 o'clock a slight bevel...

No, I'm using a brand new Franklin Armory .450BM Bolt in my Colt bolt carrier, and the barrel is mounted in a Colt upper receiver.

I will get those dimensions ASAP.

Also, the extractor and spring look good, but I do have spares I can swap in.

[Muad]

OK, the measurements I got were:

Bolt face depth = ~.127"
Bolt inner diameter = ~.475"

[Pig_Popper]

Hmmm , I'm the junior guy around here so hopefully others will speak up but it sounds like you're running the correct bolt, perhaps the bolt body is out of spec allowing the spring to push the extractor to far into the bolt face , as your picture shows.

Do you have a Grendel or 6.8 SPC or 458 Socom bolt laying around in another gun or have a buddy shooting those calibers thAt you can stick in your carrier to try out?

Worst case scenario is buy a bolt from another source and if it works fine then go back to Franklin Armory for a 99.00 credit on that bolt...

I nearly pulled the trigger on the Franklin barrel for 199.00 but research indicated the rifle length gas system to be problematic, have you shot the gun yet for function testing ?

[Hoot]

I'm at work right now, so I can't go into one of my (in)famous long answers. Your chamber may be too deep, not allowing the case to stop moving forward so that the hook can reach around the rim. That's one scenario. Second possibility is the extractor is out of spec. The rest of the causes can be more esoteric, such as a too long gas tube, a binding ejection plunger, brass that is too short and a couple of other loose ends. Loosen you gas block and slide the tube out of the receiver. Easy check to make sure the gas tube is not bottoming out in the key. Looking at all those brass shavings makes me mention the binding ejector. Brass shavings can sometimes get in alongside the plunger and bind it. IMHO, most manufactures use way too strong an ejector spring. Jeez, the ejected brass only needs to clear the receiver, not put an eye out 4 shooting stations away. I need to fabricate some diagrams to explain other things to try, which is not possible at work.

More to follow, but make those checks and see if you can upload a good image of the inside of the extractor after removing it. They come out fairly easily. I'm interested in seeing the depth of the cutout behind the hook lip.

Hoot

[Muad]

Hmmm , I'm the junior guy around here so hopefully others will speak up but it sounds like you're running the correct bolt, perhaps the bolt body is out of spec allowing the spring to push the extractor to far into the bolt face , as your picture shows.

Do you have a Grendel or 6.8 SPC or 458 Socom bolt laying around in another gun or have a buddy shooting those calibers thAt you can stick in your carrier to try out?

Worst case scenario is buy a bolt from another source and if it works fine then go back to Franklin Armory for a 99.00 credit on that bolt...

I nearly pulled the trigger on the Franklin barrel for 199.00 but research indicated the rifle length gas system to be problematic, have you shot the gun yet for function testing ?

Franklin are really good people to deal with in my experience, so if I have an actual out of spec part I'm sure they'll take care of me.

I'm running one of their 14.5" barrels that has a pinned and welded muzzle device for legality. I have not shot it yet, as I had to open up the ejection port opening, which I did this morning at about 4AM.

Thanks for the input!!

[Muad]

I'm at work right now, so I can't go into one of my (in)famous long answers. Your chamber may be too deep, not allowing the case to stop moving forward so that the hook can reach around the rim. That's one scenario. Second possibility is the extractor is out of spec. The rest of the causes can be more esoteric, such as a too long gas tube, a binding ejection plunger, brass that is too short and a couple of other loose ends. Loosen you gas block and slide the tube out of the receiver. Easy check to make sure the gas tube is not bottoming out in the key. Looking at all those brass shavings makes me mention the binding ejector. Brass shavings can sometimes get in alongside the plunger and bind it. IMHO, most manufactures use way too strong an ejector spring. Jeez, the ejected brass only needs to clear the receiver, not put an eye out 4 shooting stations away. I need to fabricate some diagrams to explain other things to try, which is not possible at work.

More to follow, but make those checks and see if you can upload a good image of the inside of the extractor after removing it. They come out fairly easily. I'm interested in seeing the depth of the cutout behind the hook lip.

Hoot

Thanks Hoot!

The gas tube is good to go, I checked that out when I installed the barrel. I've built a lot of ARs, so I've got a good handle on that stuff. The way I test to make sure that's not the issue is by inserting the stripped bolt carrier (with the gas key) into the upper receiver after I install the barrel, gas block, and gas tube. I check for any binding, etc. This is also done to ensure that the gas block (when using a low profile) is straight, because if it's not the gas tube will be off and it will sometimes bind a little in the gas key. That's not the case here. Also, since it's now cycling perfectly by hand after shimming the extractor, I'm thinking it's either the bolt, extractor, or maybe the chamber like you mention. I don't have any gauges to measure the chamber, so I'm not sure how to check that other than to fire this build.

I contacted Tony at Tromix about selling just the extractors, and he mentioned that his .458 and .450 bolts use the same extractor, and he sells the .458 extractor on his website. I might try that, or I might just contact Franklin first. The other idea was to buy a .450BM bolt from FailZero, as they have some in stock. In the end, once I get this squared away, it won't hurt to have an extra bolt laying around (I have several for my 5.56 and .277WLV guns).

Thanks again guys!!!

[TonyRumore]

Just some extractor history for you guys.......back in '95 American Firearms was making 50AE uppers and their extractors were re-worked 5.56 units. They shimmed the extractor away from the center of bolt using JB weld. When I began building big bores in '98, I basically did the same thing, but rather than using JB weld, I Tig welded up the 5.56 extractors, set them up in a holding fixture and remachined them one at a time on my Bridgeport using a carbide woodruff keyset cutter. I sold the extractors and other big bore parts to a couple other companies that were assembling 50AE uppers at the time. Eventually the demand was great enough to just scrap the 5.56 extractor rework and we moved on to simply CNC machining them from S7 bar stock, with subsequent heat treating.

Tony Rumore
Tromix