Excessive bullet runout caused by magazine feed?

[TaperPin]

I would chock this up to nonsense, but a long bullet stick out does create more torque, so I’m thinking out loud here. I have a 300-something hunting rifle in the works, but it has to feed from a magazine.

I read something from a 300 prc shooter that the long bullet stick out was causing ridiculous runout when fed from the magazine to the point it’s only usable as a single shot. With the increase in long heavy for caliber bullets and extra long magazines allowing longer than usual overall length, is this a really big issue with the new trend in cartridge design, or is that person’s experience most likely to do more with insufficient bullet/neck contact (maybe the boat tail was into the neck)? Hard to believe a saami throat in the prc would be so long that it’s become a serious fundamental flaw even with long heavy bullets, but I only have experience with cartridges forced to have bullets crammed way down in the case by short magazines.

The other variable is the magazine the fellow had is a center feed detachable and I can imagine a stiff spring in a full mag and overly cautious feed lips putting more than normal upward pressure on the bullet as it’s pushed up the feed ramp.

I’d enjoy hearing thoughts on any calibers that have had issues.

 

[jackieschmidt]

I guess the best way to find out is check the runnout on a loaded round, then place the round in the magazine and with the bolt stripped, feed it into the chamber. Then take it out and check it again.

Logic would dictate that the lighter the neck tension, the more susceptible loaded round would be to distortion.

Considering multitudes of successful shooters are shooting really long bullets out of magazines, it might not be a problem.

 

[TaperPin]

I guess the best way to find out is check the runnout on a loaded round, then place the round in the magazine and with the bolt stripped, feed it into the chamber. Then take it out and check it again.

Logic would dictate that the lighter the neck tension, the more susceptible loaded round would be to distortion.

Considering multitudes of successful shooters are shooting really long bullets out of magazines, it might not be a problem.

I agree there’s nothing as good as testing it - a 300 rum magazine has been ordered and I definitely want to see with my own eyes that a loaded 300 prc round is durable enough to feed through my rifle.

A second 300 prc guy told me, “Of course feeding through the magazine increases runout.” Which makes me feel like it’s a candid camera setup and hopefully a bald guy will come out and say it’s all been a joke. Or maybe this is more of a thing with the center feed magazines everyone is so in love with?

 

[K22]

You said hunting rifle, right?

With that caliber you will probably be hunting a large animal with a large vital area, right? Thus, would run out be a factor?

For a hunting reload, you should be seated well of the lands to prevent a bullet becoming stuck in the lands in the field when you extract an unspent round. Thus, I would think there would be enough bullet in the case to prevent any excessive distortion.

If the neck tension is so fragile that feeding causes a distortion would chambering the round straighten it sufficiently?

As others have said, measure a feed round to determine if there is an affect. If so, see if it matters with shots on target relative hunting accuracy for big game. I doubt if you'll miss a deer, beer, or elk due to round out.

 

[akajun]

An old highpower shooter taught me this
Take your best no runout reloads
Loaded long or mag length
Put them in the chamber, especially in a semi auto, and release the bolt
Take em out and measure them
Then do the same but loaded from a mag
Measure them
All will have added runout and you might have a few “ bananas”
Yet people are still shooting amazing scores, cleaning targets in spite of this

 

[Coyotefurharvester]

This is assuming the cartridge base is held very tight to the bolt face ?

 

[J.d. Popkes]

I think the whole bullet runout concentricity thing has been put to bed. There’s been tests/videos showing how little it matters.

Concentricity gauges are paperweights collecting dust these days, right?

 

[Dgd6mm]

I'm not going to sweat the small stuff. Especially when I'm running a rifle fast and furious while still laying down very acceptable groups at various distances. AICS type mags always, unless shooting FTR with one of my single shots.

 

[jelenko]

FWIW. I have 223 dummy rounds that I've used to practice 'rapid fire' for XTC. They have been rapidly cycled through a bolt action hundreds of times. I just measured runout on 5 of them. The runout is <1 thousandths on all, which is just a smidgen more than what I get on regular rounds.
The dummy rounds are all loaded to 223 mag length [~ 2.250] with a neck tension of 3 thousandths.

 

[BoydAllen]

I would chock this up to nonsense, but a long bullet stick out does create more torque, so I’m thinking out loud here. I have a 300-something hunting rifle in the works, but it has to feed from a magazine.

I read something from a 300 prc shooter that the long bullet stick out was causing ridiculous runout when feed from the magazine to the point it’s only usable as a single shot. With the increase in long heavy for caliber bullets and extra long magazines allowing longer than usual overall length, is this a really big issue with the new trend in cartridge design, or is that person’s experience most likely to do more with insufficient bullet/neck contact (maybe the boat tail was into the neck)? Hard to believe a saami throat in the prc would be so long that it’s become a serious fundamental flaw even with long heavy bullets, but I only have experience with cartridges forced to have bullets crammed way down in the case by short magazines.

The other variable is the magazine the fellow had is a center feed detachable and I can imagine a stiff spring in a full mag and overly cautious feed lips putting more than normal upward pressure on the bullet as it’s pushed up the feed ramp.

I’d enjoy hearing thoughts on any calibers that have had issues.

Years ago my friend had a custom hunting rifle built in 7mm WSM. It feeds from a magazine with heavy bullets and he has had no issues with how is shoots, and he takes some long shots. Typically he will figure out how to get in bipod prone. We annealed his cases to get more uniform shoulder bump but not as soft as I see on YouTube. We were able to find a middle ground by working up to the point where we had the bump uniformity while maintaining necks of sufficient hardness to work with the heavy bullets out of a magazine. It is a two torch flame annealer. A friend runs 600 yard matches in Colorado, and they have a tactical class. Those guys shoot full built long range rifles with the only difference being a magazine, and recently they have shot a little better than the single shots.

 

[Alex Wheeler]

Yes, this is a real problem. The issue is not really from the runout but from the neck tension. When you induce that runout from cycling the round you have also loosened up your neck tension. This is why you take to time to tune the spring and mags so that this does not happen. A properly tuned center feed box is very gentle on the ammo.

 

[TaperPin]

Yes, this is a real problem. The issue is not really from the runout but from the neck tension. When you induce that runout from cycling the round you have also loosened up your neck tension. This is why you take to time to tune the spring and mags so that this does not happen. A properly tuned center feed box is very gentle on the ammo.

Very interesting - that’s one of those things that as soon as I heard it put that way the light bulb went off and it makes more sense now.

Center feed. Hmm... Twenty years ago if an elk hunting buddy took two shots with his 8mm Rem astro blaster, then stopped, turned his rifle upside down and popped the floor plate to reload, I would have smacked the back of his head and said, “Are you high - what the hell are you doing!?”

I’ve always been intimidated by the rather mysterious geometry & nature of a well feeding magazine - staggered magazine - so my deep dive into those has been long overdue and I’m enjoying it. After the fun & newness wears off of TIGing partial action rails to a dozen different magazines I’ll be more receptive to better performance from a single feed. It’s a lot like women - you have to date a number of high maintenance, crazy, overly fun & arnery ones before accepting the one should have.

 

[BoydAllen]

Some time back, I received a stock as a writing project. It was set up with a detachable magazine that was furnished. Trying the magazine for feed (.243 SA Rem.) with some factory pointed soft point ammo, I could see that the exposed lead was heavily marked by the feed ramp in the action, which of course I did not like. Since I had played with metal magazines, I thought that I could do the same with this plastic one, and when I finished it would feed one round perfectly, but when it was on top of others I found that I had ruined the magazine. Doing a little research on line, I found that there was another brand that had high marks for how it fed, and ordered one. With it, the bullet went into the chamber without hitting the feed ramp. To me the difference had to be the different shapes of the followers. My point in telling this story is that your rifle may benefit from some fiddling with or trying different followers.

 

[TaperPin]

Some time back, I received a stock as a writing project. It was set up with a detachable magazine that was furnished. Trying the magazine for feed (.243 SA Rem.) with some factory pointed soft point ammo, I could see that the exposed lead was heavily marked by the feed ramp in the action, which of course I did not like. Since I had played with metal magazines, I thought that I could do the same with this plastic one, and when I finished it would feed one round perfectly, but when it was on top of others I found that I had ruined the magazine. Doing a little research on line, I found that there was another brand that had high marks for how it fed, and ordered one. With it, the bullet went into the chamber without hitting the feed ramp. To me the difference had to be the different shapes of the followers. My point in telling this story is that your rifle may benefit from some fiddling with or trying different followers.

That’s good advice - I’m having good luck sorting things out. It’s been fairly easy to snap overhead photos of rifles in various calibers to see the factory receiver rails, which don’t vary as much as I had assumed. It’s somewhat predictable that fat cartridges have corresponding fatter magazines, 223 magazines are thinner, short cartridges need magazine blocks to bring the cartridges to the front of the magazine, and all of them are quite dependent on the magazine follower and geometry between cases providing enough upward pressure, especially toward the front.

There is a new problem I did not anticipate. The plan was for a modest range of cartridges, but once you are scanning for barrels the number of interesting cartridges expands, many for less than a fast food lunch, and some custom barrels with plenty of life for the price of a decent steak dinner. Same for stocks. Same for scopes.