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Posted: 11/3/2025 12:13:17 AM EDT
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I have several A2 service rifles I want to convert to flat tops, the problem is they have rifle barrel extensions. I suppose I could have a pro modify the current rifle extensions to m4 specs. I could have someone that is well stocked with m4 barrel extensions play with their inventory until one works and headspaces properly. What does the community think? |
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https://ar15discounts.com/products/dirty-bird-ar-15-stripped-upper-receiver-no-feedramps/ Edit: sorry, didn't notice they were already OOS  Maybe try Model1Sales. I have a .22LR upper of theirs from 10+ years ago that is a flat top without M4 feedramps. They don't list that upper stripped on their site but they still sell .22 upper halves so they may still use them for that. I'd give them a call. Maybe they'd be willing to sell one stripped (if they still have them). It would be cheaper than paying someone to modify feedramps or spend the time trying extensions until one headspaces. |
| In the past both Aero Precision and DS Arms sold flattop uppers without M4 ramps, but neither list them at the moment. In the distant past PSA had some FN overrun or blem or something A4 uppers that didn't have ramps. |
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I'd just put them on an M4 upper. Just make sure that the extension face is not poking out and providing a lip for the point of a projectile to hang up on. If it is, you can use a shim from Bison Armory to make it seat out a little further and provide clearance. For a gun used as a SR in competition, it's a non issue IMO. |
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Originally Posted By bpm990d: I'd just put them on an M4 upper. Just make sure that the extension face is not poking out and providing a lip for the point of a projectile to hang up on. If it is, you can use a shim from Bison Armory to make it seat out a little further and provide clearance. For a gun used as a SR in competition, it's a non issue IMO. Just because it's for service rifle competition, doesn't mean it doesn't have to be 100% reliable. SR rifles can serve as Designated Marksman rifles in a pinch as well. |
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Originally Posted By borderpatrol: Just because it's for service rifle competition, doesn't mean it doesn't have to be 100% reliable. SR rifles can serve as Designated Marksman rifles in a pinch as well. Do you shoot your service rifle in full auto? If so get the correct upper. |
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Originally Posted By bpm990d: Do you shoot your service rifle in full auto? If so get the correct upper. Shooting full auto has nothing to do with the problems created by using a rifle barrel extension in a M4 ramped upper. The rifle barrel extension has a hard stop that the M4 ramps force bullets into. Rifle barrel extensions have to be used in uppers that don't have the M4 ramps, there is no getting around it. Hand grinding the rifle barrel extension so that it mates with M4 ramps is one option. That's the option I am least interested in. I think Larue has a four-picture explanation on their website that explains what works and what doesn't. Standard rifle barrel extensions in an M4 upper is the only option that fails. |
| GPC has 3 in stock. Used and ~$73, so, the question is, how bad do you want one? |
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Originally Posted By borderpatrol: Shooting full auto has nothing to do with the problems created by using a rifle barrel extension in a M4 ramped upper. The rifle barrel extension has a hard stop that the M4 ramps force bullets into. Rifle barrel extensions have to be used in uppers that don't have the M4 ramps, there is no getting around it. |
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Originally Posted By Bebop_941: https://i.ibb.co/Wvc71L2n/proxy-image.jpg also LaRue used to make a rifle feed ramp flat top IIRC. |
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Originally Posted By HighpowerRifleBrony: If the bullet jams in a rifle/M4 situation, how would it also not jam in a rifle/rifle situation? Either the tip rides up the extension's ramp or jams the nose into the receiver. Originally Posted By HighpowerRifleBrony: Originally Posted By borderpatrol: Shooting full auto has nothing to do with the problems created by using a rifle barrel extension in a M4 ramped upper. The rifle barrel extension has a hard stop that the M4 ramps force bullets into. Rifle barrel extensions have to be used in uppers that don't have the M4 ramps, there is no getting around it. Huh? Think you are misunderstanding things. M4 receiver ramps paired with a rifle barrel extension means the bullet tip wedges itself into the gap between the receiver and barrel extension- no good. Rifle extension extends out further than the top of the M4 receiver ramp. Rifle receiver (no ramp at all) paired with rifle barrel extension is how millions of M16’s and AR’s have been made. It was literally designed that way. There is no gap like in the first example. Rifle receiver paired with an M4 barrel extension on the other hand will work OK, just not ideal, especially for F/A fire in short M4 length barrels. Plenty of early AR’s with shorter barrels have rifle receivers and rifle style barrel extensions, it wasn’t until the M4 model actually came about that it was decided the M4 receiver ramp was needed to help improve feeding. |
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| After i couldnt find the upper you are looking for, I had my A2 service rifle converted to flat top SR with M4 ramps by White Oak armory this spring. They replaced the barrel extension. |
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Originally Posted By slappomatt: I ran a rifle with the "bad" config for almost a year. never had an issue with it. also LaRue used to make a rifle feed ramp flat top IIRC. Originally Posted By slappomatt: Originally Posted By Bebop_941: https://i.ibb.co/Wvc71L2n/proxy-image.jpg also LaRue used to make a rifle feed ramp flat top IIRC. You're correct that the "bad" configuration can work if the round is oriented to feed from the magazine onto the barrel extension's feed ramp. But it also has a higher potential for failure. Use a different magazine or ammo that changes the orientation and now it doesn't work. The same can be true using rifle or M4 feed ramps with a non-feed ramp upper if the tip of the round hits low enough on the upper to completely miss the feed ramps. This is not particularly common but can occur when using rounds with a longer OAL. It's the primary reason M4 feed ramps were developed to accommodate the OAL of M855. However, if the round hits closer to the transition point between the upper and barrel extension, the tip of the round can still deflect onto the feed ramps. Not ideal but it's better than the "bad" set-up, which creates a ledge that effectively captures the tip of the round and prevents feeding entirely. All this to say, the "bad" set up has the smallest margin for error when it comes to orientation of the round from the magazine to the feed ramps. Sure it can work, but there is no reason to build a potential point of failure into your rifle and hope for the best. |
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Originally Posted By JoeDevola: Didn't some idiot around here once use a Dremel to modify the ramps in a rifle extension to mate up with M4 ramps in an upper? That was a pretty standard occurrence for a while. Quite a few tutorials and DIY threads. |
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Originally Posted By JoeDevola: Didn't some idiot around here once use a Dremel to modify the ramps in a rifle extension to mate up with M4 ramps in an upper? Did he do a shit job or something? Colt used to dremel their feed ramps and did a worse job in some cases then alot of DIYers. |
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Originally Posted By tac556: Huh? Attached File |
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Originally Posted By Bebop_941: Did he do a shit job or something? Colt used to dremel their feed ramps and did a worse job in some cases then alot of DIYers. Originally Posted By Bebop_941: Originally Posted By JoeDevola: Didn't some idiot around here once use a Dremel to modify the ramps in a rifle extension to mate up with M4 ramps in an upper? Did he do a shit job or something? Colt used to dremel their feed ramps and did a worse job in some cases then alot of DIYers. Yes, it looked like ass. |
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Originally Posted By HighpowerRifleBrony: With good magazines, how does the bullet tip jam? https://www.ar15.com/media/mediaFiles/379478/Feedramps_jpg-3655193.JPG I agree with you that all 4 configurations will work if the feed angle is correct. My only point of contention is that the rifle extension paired with m4 feed ramps offers the smallest margin for error. To me, it doesn't make sense to choose the configuration that has the highest potential for failure compared to all of the available alternatives. It would be interesting to see through extensive testing how reliable that config can be. I suspect it would be more sensitive to a wider selection of magazines, cartridges with a greater OAL, guns with a faster cycle rate and adverse conditions (or any various combinations of the above). I also suspect it would do fine with M193 from pmags when its 70 degrees and sunny outside. It just depends on your specific performance criteria. |
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Originally Posted By JoeDevola: Yes, it looked like ass. Originally Posted By JoeDevola: Originally Posted By Bebop_941: Originally Posted By JoeDevola: Didn't some idiot around here once use a Dremel to modify the ramps in a rifle extension to mate up with M4 ramps in an upper? Did he do a shit job or something? Colt used to dremel their feed ramps and did a worse job in some cases then alot of DIYers. Yes, it looked like ass. 
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Originally Posted By borderpatrol: Combatdiver posted in another thread the proper part number for a rifle extension flat top upper if anyone else cares to reference it. General Mfg. 1UH06 1005-01-454-9880 Currently out-of-stock... Those blems went OOS quick. I've been checking to see whether they restock weekly but no joy. |
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Originally Posted By JoeDevola: Didn't some idiot around here once use a Dremel to modify the ramps in a rifle extension to mate up with M4 ramps in an upper? Colt, Rock River and Double Star for sure. Likely others. I have a 10-1/2" example. It works great. It took years for M4 ramps to go from "Whut?" to "Necessity" for Semi-Auto carbines and rifles. What worked fine for decades became, "I'm surprised you haven't died". |
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