Bolt drags on mag

[vigildom7]

I apologies if this question has been asked before but I can't find anything.
I picked up a Bighorn origin action and have it mounted up in a Mcmillan A5 with the what I believe is surgeon BM.
With the magpul AI mags I get a slight bolt drag on the feed lips. But when a slight upward pressure on the mag such as positional shooting. It pushes the feed lips into the raceway preventing the bolt going forward and stripping off a round.
But with a metal AICS mag I get a little drag both with and without pressure on the mag. Is the dimensions on the polymer mag that much more to prevent bolt travel?
I used both magpul AICS mags and the metal AICS mags in my krg bravo and r700 with out issue.
Any idea on how to remove the drag?

 

[ThePretzel]

Almost all DBM's and chassis will hold the magazine in such a way that the bolt binds if you put upwards pressure on an AICS magazine or set the rifle down on top of the magazine. I have yet to encounter one that would cycle 100% properly if you set the weight of the rifle entirely on the magazine.

The feed lips on the Magpul AICS mags are thicker, because of their polymer construction, and will accordingly be more likely to catch against the bolt. You can adjust the clearance for the bolt by filing down the feed lips (on the Magpul) or by filing/bending feed lips to tweak the fit for your rifle (on the metal AICS).

The metal magazine will be easier to tune because you can bend the feed lips slightly outwards. This improves clearance for the bolt while also making the rounds sit higher (slightly easier to strip). If you overdo it the rounds will start popping out early, but it doesn't take much to improve it. It's similar to tweaking the magazine on a 1911 to ensure proper feeding, since there will be variations in sheet metal parts (the magazines) and fitment between different actions and chassis/DBM systems.

Another thing I've seen people do is trim a small angle into the rear of the feed lips, which acts a bit like a ramp as the bolt comes forwards to push the magazine back down if it's moved far enough up that it's binding the bolt itself. The drag on the feed lips would remain when you did this, however.

 

[vigildom7]

Almost all DBM's and chassis will hold the magazine in such a way that the bolt binds if you put upwards pressure on an AICS magazine or set the rifle down on top of the magazine. I have yet to encounter one that would cycle 100% properly if you set the weight of the rifle entirely on the magazine.

The feed lips on the Magpul AICS mags are thicker, because of their polymer construction, and will accordingly be more likely to catch against the bolt. You can adjust the clearance for the bolt by filing down the feed lips (on the Magpul) or by filing/bending feed lips to tweak the fit for your rifle (on the metal AICS).

The metal magazine will be easier to tune because you can bend the feed lips slightly outwards. This improves clearance for the bolt while also making the rounds sit higher (slightly easier to strip). If you overdo it the rounds will start popping out early, but it doesn't take much to improve it. It's similar to tweaking the magazine on a 1911 to ensure proper feeding, since there will be variations in sheet metal parts (the magazines) and fitment between different actions and chassis/DBM systems.

Another thing I've seen people do is trim a small angle into the rear of the feed lips, which acts a bit like a ramp as the bolt comes forwards to push the magazine back down if it's moved far enough up that it's binding the bolt itself. The drag on the feed lips would remain when you did this, however.

Is there any guide (video) or instructions on bending the feeds lips?

 

[ThePretzel]

Is there any guide (video) or instructions on bending the feeds lips?

Grab a pair of reasonably long needlenose pliers. You'll want them long enough that you can pinch the entire length of the feed lip between them.

Take the pliers and clamp the feed lip at the very top of the lips along the entire length of the feed lip. Bend them out a little ways and see if it works for you. If you bend too far and the magazine has problems, do the same thing but bend them back in.

When you're done bending make sure to smooth up the inside of the feed lips (where the brass contacts them and where your pliers were clamping) using some scotch brite. Most pliers have textured jaws and will leave little marks that can either scratch up your brass or even sometimes catch on the brass and prevent you from being able to properly feed rounds, so just smooth it out and polish it up when you're finished.

 

[KZP]

You can also put a couple layers of masking tape on the magazine or pliers jaw to reduce galling.

 

[spife7980]

Is there any guide (video) or instructions on bending the feeds lips?

Follow The pretzels guide on how to do it and KZPs recommendation of a buffer material to reduce metal scrathing is good as well.

I bet your old actions dragged a bit too only you just didnt notice it as a problem. I never noticed mine until someone pointed it out at which point I tested it and sure enough, it bound them up. Still not a problem for me though.

While it was in relation to rounds diving in the mag, the general set up is still the same, here is Longrifles Inc recommendations on how the round should be presented by the magazine in the action, a figure 8. The top loop being the bore and the bottom loop being the primer, tangent to one another when viewed from the rear.

"Booger hooking" the feed lips is the last resort. The problem is insufficient case overlap with the bolt face. Simply to mean not enough of one in contact with the other. You fix this one of two ways. Either make the action sit lower in the stock or make the floor metal present the magazine further into the receiver bore.

When the DBM is sitting where it "should" (presenting well on the bottom of the stock) its cosmetically painful to sink it. Just looks like poo afterward. What I do in this instance is pull the release lever and either make a new one (slightly longer) or put a stitch of TIG weld on the original to grow it some. Then machine/fit to make it run again.

The ideal arrangement is the "upside down figure 8". The receiver bore is one of the arcs in the 8. The primer pocket is the other. When those two circles are tangent to one another, things work as they should. You verify this by pulling the bolt, gassing up a magazine, and inserting it. Now look down the ass of the receiver. If you can see a trace edge of the primer pocket just starting to invade the receiver bore, your golden. That gun should run like a scalded dog.

The one exception to this is ARC magazines. On occasion they'll hang up the last round. We've adopted a little alteration to the follower to help mitigate this.

Happy to help. Good luck.

 

[Sogan]

Is there any guide (video) or instructions on bending the feeds lips?

 

[wade2big]

OP, your 700 would bind completely with upwards pressure with a mag pull mag I promise you. This can’t be fixed with the 700 and magpul mags. Filing the feedlips may solve the dragging problem with your origin on a free hanging mag. You would have to push it upwards and see if enough material can be removed to where the bolt won’t drag and the rounds will still be contained by the feedlips. My axiom action worked perfectly with a few swipes of a file. Magpul mags are a crapshoot with certain actions. Let us know for sure with the origin.

Remington 700 actions and my axiom action would cycle with no drag with unmodified ai and accurate mags with pressure on the mags. No modification required.

 

[vigildom7]

Hey everyone just an update I found where my bolt was striking on the magpul mag. and slightly filed and rounded out that spot. Now those mags work flawless with out removing to much to weaken the feed lips.

 

[KZP]

Great, good to hear. Always nice when a problem ends up being simple to fix.

 

[supercorndogs]

All my 700s with AI mags run fine with the full weight of the rifle on a metal mag or magpul mag. They stop on the bottom of the action before they can get high enough to interfere with the bolt.

 

[SuperSneakySniper]

My Impact action never had this issue in an MPA chassis, but it does in the Magpul Pro chassis.
I filed the feed lips on my metal AICS mag using a long steel file, then smoothed the edges out with a steel nail file. Also, I actually used a bench vise to bend the feed lips inwards just to increase retention on the cartridges. Im not sure if that's how it's supposed to be done, but it worked out for me. Cartridges are retained very well, feeds fine, and no matter how much pressure I put on the mag, my bolt doesnt touch the feed lips.
I didnt use any guides, and im a moron, so if i can do it, anyone can. Happy with my results thus far.

EDIT: And to show just how much of a moron I am, I made this post without realizing it was already resolved... Go me!
Anyways good to hear it's settled!

 

[wade2big]

All my 700s with AI mags run fine with the full weight of the rifle on a metal mag or magpul mag. They stop on the bottom of the action before they can get high enough to interfere with the bolt.

Double check your magpul mags. The metal mags work. The magpul mags will push up and interfere with the bolt and filing wont fix it. I have yet to see a 700 that will work correctly with magpul mags.

 

[supercorndogs]

Double check your magpul mags. The metal mags work. The magpul mags will push up and interfere with the bolt and filing wont fix it. I have yet to see a 700 that will work correctly with magpul mags.

I have yet to see one that doesn't..

 

[wade2big]

I have yet to see one that doesn't..

I have three in my safe. By the multiple threads on this topic on just this website alone, it seems your rifle is the exception. Maybe it is out of spec in all the right places. It would be hard to imagine that your 700 is built differently where magpul mags wouldnt over insert to the point where the rifle is inoperable as 700 actions are relatively the sMe with no major revisions through the year that I am aware of.

Its not an action issue, its the shape of the magpul mags. Even the Remmys that ship with the magpul mags in the magpul stocks wont cycle with pinky pressure upwards on the mag.

Maybe triple check with those plastic ones. Actually grab the rifle, insert the mag and push up on the thing. Cycle the bolt and check back in. Dont say you checked, actualy do it then post back here. I would be interested in the results whether I am right or wrong. I say this being completely sincere. Im not trying to be an ass. I am just doubtful that you actually checked after you read this thread given the results you posted. I hope you are sincere with your answer as well.

 

[supercorndogs]

I have three in my safe. By the multiple threads on this topic on just this website alone, it seems your rifle is the exception. Maybe it is out of spec in all the right places. It would be hard to imagine that your 700 is built differently where magpul mags wouldnt over insert to the point where the rifle is inoperable as 700 actions are relatively the sMe with no major revisions through the year that I am aware of.

Its not an action issue, its the shape of the magpul mags. Even the Remmys that ship with the magpul mags in the magpul stocks wont cycle with pinky pressure upwards on the mag.

Maybe triple check with those plastic ones. Actually grab the rifle, insert the mag and push up on the thing. Cycle the bolt and check back in. Dont say you checked, actualy do it then post back here. I would be interested in the results whether I am right or wrong. I say this being completely sincere. Im not trying to be an ass. I am just doubtful that you actually checked after you read this thread given the results you posted. I hope you are sincere with your answer as well.

Not rifle, rifles. With my weight on them, they make the bolt sticky. Most of the AI mag interfering with the bolt problems I have seen seemed to stem from AI mag chassis with an AW cut action.

Anyone who has used their magpul mags for a while test this? Perhaps over the last thousands of rounds through my magpul mag has wore in a little. If I had to worry about weight on my mag jamming up the gun, that mag would be in the trash faster than you can say shit. Espspecialy if metal mags don't do it.

I thought I had a second unused magpul mag somewhere to try out, but I can't find it. My sample size is many rifles but only 1 magazine with 4-5k through it, in about a dozen different actions, chassis, and pillar bedded stocks.

 

[wade2big]

Thats weird. To get the magpul mags to run in my 700s you would have to grind off the feed lips completely and good luck keeping a round in the magazine like that. The bolt hits the base of the feedlips. Magpul mags work in my curtis axiom with just a few swipes of the file. Just slight bolt drag is all. I would post a picture to show you but all my magpul aics mags have been sold off for that reason. I want mags that work in all my rifles just as you do. They do feed much more smoothly than metal mags.

Im curious to hear if any other guys are having any luck getting the magpuls to work. I have already read many threads of guys having the same issues as mine with 700s and other actions like the curtis vector.

 

[supercorndogs]

Thats weird. To get the magpul mags to run in my 700s you would have to grind off the feed lips completely and good luck keeping a round in the magazine like that. The bolt hits the base of the feedlips. Magpul mags work in my curtis axiom with just a few swipes of the file. Just slight bolt drag is all. I would post a picture to show you but all my magpul aics mags have been sold off for that reason. I want mags that work in all my rifles just as you do. They do feed much more smoothly than metal mags.

Im curious to hear if any other guys are having any luck getting the magpuls to work. I have already read many threads of guys having the same issues as mine with 700s and other actions like the curtis vector.

It is undoubtedly a wear in issue with mine. You can see where my bolt has worn away the offending plastic. I bet it was a fluted bolt cutting at it. I bet if i did it a little more it would not bind up the bolt anymore.

 

[ThePretzel]

Anyone who has used their magpul mags for a while test this? Perhaps over the last thousands of rounds through my magpul mag has wore in a little. If I had to worry about weight on my mag jamming up the gun, that mag would be in the trash faster than you can say shit. Espspecialy if metal mags don't do it..

I've put a couple thousand rounds through a Magpul AICS 10 rounder and it still does it, both with a Christensen TFM (whatever bottom metal they use, I think it's their own) and with my custom Nucleus build in an XLR Envy. Both would also cause factory standard Accurate Mags to have the same issues when the rifle is set down or pressed down on top of the magazine (it's less noticeable in the CA rifle, but that's because it's less than half the weight of the other rifle - they're equal when I'm pressing down on both guns from the top of the scope).

I think it's a function of how much wiggle room the magazine has based on the bottom metal or chassis. My XLR and the CA bottom metal allow the magazine to shift upwards a bit when pressure is applied, so I just bent the feed lips out slightly on my Accurate Mag's to prevent that from being an issue. Haven't messed with the Magpul ever though. Interestingly enough I don't have the same issue with ARC mags in either action, but I also am less likely to press on the magazine in the first place. I'll see if I can measure the feed lip width of a factory Accurate Mag, a factory ARC mag, and my Magpul mag to see if there's any big differences.

 

[wade2big]

Its not a bottom metal issue at all. The bottom metal is just a funnel with a latch to keep the mag from falling out. Nothing stops upward travel of the mag except the action. Metal mag feed lips can be manipulated just like you said to a degree. Plastic feedlips can only be shortened with a file. Sometimes thisnis enough with certain actions. Other times it isnt.

 

[Saltyag15]

Sorry to resurrect an old thread, but I just wanted to say thank you to everyone who offered advice on this. I was having these exact issues with my new Terminus Apollo/MPA chassis/magpul mags. I was getting pretty considerable bolt drag across the tops of the mags, causing it to be pretty stiff.

I took a nail file and slowly started taking some off the top of the mag, checking it regularly by putting it back in the gun. Once the bolt friction minimized, I put some rounds in the mag to ensure they would feed properly. Everything works perfect now. Glad to know it was something so simple!