Need suggestions on increasing neck tension

[SWThomas]

So I loaded up a dummy round tonight to "test" the neck tension on my 308 loads for my GAP-10 (AR-10). I placed it in the magazine and allowed the bolt to slam forward, stripping it off the magazine and chambering it. I measured the OAL with my digital caliper before and after this test. Afterward the OAL had grown by 0.002. If this is normal and acceptable, I'll carry on. If not, how can I increase neck tension to avoid inertia from pulling these bullets from their cases?

I'm currently using a Dillon 308 steel sizing die. I measured the expander button and it measures 0.306. I conducted this test with resized brass and a 175g SMK BTHP.

Thanks!

 

[338 Mollett]

Interesting post,I don't think .002 is gonna hurt one way or the other with an ar 10 or even a bolt gun. But the question is that .002 going to be consistent ?I would be afraid of the one neck tension that did not hold the bullet as tight and either changed my poi or jammed it in the lands if I had to eject an unfired cartridge maybe pulling the bullet out and getting powder everywhere etc.

 

[BigDMT]

Need to crimp the bullets. Always a good idea to crimp bullets in any semi-auto rifle. I always full size the brass and roll crimp the bullets in the ammo for my 5.56 and 6.8 SPC AR-15 rifles

 

[SWThomas]

Interesting post,I don't think .002 is gonna hurt one way or the other with an ar 10 or even a bolt gun. But the question is that .002 going to be consistent ?I would be afraid of the one neck tension that did not hold the bullet as tight and either changed my poi or jammed it in the lands if I had to eject an unfired cartridge maybe pulling the bullet out and getting powder everywhere etc.

It would have to be pretty loose to jam the bullet into the lands. Being that my seating depth is restricted by magazine length, the bullets are pretty far from the lands.

 

[SWThomas]

Need to crimp the bullets. Always a good idea to crimp bullets in any semi-auto rifle. I always full size the brass and roll crimp the bullets in the ammo for my 5.56 and 6.8 SPC AR-15 rifles

I do that with my AR-15 loads because they're for blasting. But crimping a match bullet is contrary to everything I've read about precision shooting.

 

[BigDMT]

Then there may not be much you can do. You can try crimping to see. You might still get very accurate loads with crimping. If you are only seeing .002" jump from chambering, I'd bet a ever so slight roll crimp over the tip of the neck is all you'd need

Otherwise, you could take about 5 bullets and soak them in a small tray of paint thinner to remove any oils on the jacket. Then seat them and test each one by chambering and measuring to see if it helps stop the bullet jump from inertia.

 

[spclark]

None of the competition shooters I know crimp match ammo. Mind, these aren't folks using 308-chambered gas guns either.

I doubt whether 0.002" OAL "growth" will affect accuracy more than crimping case necks, but then I have no idea how far you're jumping bullets seated to mag-length either.

What's important is: do rounds grow enough while loaded in the magazine to interfere with proper feeding? That can be a problem....

As for boosting neck tension: simple way is lose the expander button. If the neck diameter you get then won't permit easy bullet seating, your sizing die is working the brass too much anyway.

 

[BigDMT]

None of the competition shooters I know crimp match ammo. Mind, these aren't folks using 308-chambered gas guns either.

I doubt whether 0.002" OAL "growth" will affect accuracy more than crimping case necks, but then I have no idea how far you're jumping bullets seated to mag-length either.

What's important is: do rounds grow enough while loaded in the magazine to interfere with proper feeding? That can be a problem....

As for boosting neck tension: simple way is lose the expander button. If the neck diameter you get then won't permit easy bullet seating, your sizing die is working the brass too much anyway.

Good point. A neck bushing die (and proper bushing) with no expander ball would probably help as well.

 

[BoydAllen]

I think that you are making this too complicated. Get another expander ball, mount it on the decapping stem, chuck that in a corded drill and carefully polish the expander down .001 and do another test, and then take off another .001 and try it again. I don't really think that you have a problem unless you have the bullets so far into the lands that one would be pulled if you had to unload. In this case, the bullet is probably not moving until the bolt is locked, so it cannot interfere with that (I think). You may be trying to fix something that is not a problem.

 

[Jeffvn]

you don't say what neck tension you are currently using. I ran my 260 DPMS with 3-4 thou of neck tension. I had no problems with slam-based growth or contraction on my Berger 130s.

Another way to check if you have enough tension is to load a magazine, shoot most of the rounds, then pull and measure the remaining rounds for seating length. If they get shorter from being inside the magazine you'll want to add touch more neck tension (different bushing on your full-size bushing die).

Jeffvn

 

[SWThomas]

None of the competition shooters I know crimp match ammo. Mind, these aren't folks using 308-chambered gas guns either.

I doubt whether 0.002" OAL "growth" will affect accuracy more than crimping case necks, but then I have no idea how far you're jumping bullets seated to mag-length either.

What's important is: do rounds grow enough while loaded in the magazine to interfere with proper feeding? That can be a problem....

As for boosting neck tension: simple way is lose the expander button. If the neck diameter you get then won't permit easy bullet seating, your sizing die is working the brass too much anyway.

I would try that, but most of the brass fired from this gun gets dinged up case mouths. The ball is really necessary to open them back up and make them round again.

 

[SWThomas]

I think that you are making this too complicated. Get another expander ball, mount it on the decapping stem, chuck that in a corded drill and carefully polish the expander down .001 and do another test, and then take off another .001 and try it again. I don't really think that you have a problem unless you have the bullets so far into the lands that one would be pulled if you had to unload. In this case, the bullet is probably not moving until the bolt is locked, so it cannot interfere with that (I think). You may be trying to fix something that is not a problem.

That sounds like a pretty good idea. Any recommendations on what to polish a carbide expander ball with?

 

[SWThomas]

you don't say what neck tension you are currently using. I ran my 260 DPMS with 3-4 thou of neck tension. I had no problems with slam-based growth or contraction on my Berger 130s.

Another way to check if you have enough tension is to load a magazine, shoot most of the rounds, then pull and measure the remaining rounds for seating length. If they get shorter from being inside the magazine you'll want to add touch more neck tension (different bushing on your full-size bushing die).

Jeffvn

I said in the OP that the expander ball is 0.306. I've verified that it is in fact expanding the case mouths to that diameter. Should I be measuring something else?

 

[Turbulent Turtle]

I gave my answer to your question in your other thread.

 

[SWThomas]

I gave my answer to your question in your other thread.

Thanks!

 

[jtbewebber]

Just an idea, I used it when I loaded for my AR-15. If you are not seating the bullets to the cannelure then I wouldn't roll crimp. Get a Lee Factory Crimp die. It didn't effect my accuracy at all and should eliminate your problem.

 

[jlow]

I think that you are making this too complicated. Get another expander ball, mount it on the decapping stem, chuck that in a corded drill and carefully polish the expander down .001 and do another test, and then take off another .001 and try it again. I don't really think that you have a problem unless you have the bullets so far into the lands that one would be pulled if you had to unload. In this case, the bullet is probably not moving until the bolt is locked, so it cannot interfere with that (I think). You may be trying to fix something that is not a problem.

That sounds like a pretty good idea. Any recommendations on what to polish a carbide expander ball with?

One of the best polish I have used is "No7 Rubbing Compound" from Ace Hardware. The stuff is a paste and will shine your ball to a mirror finish.

Keep in mind that it is a bit too fine to take it down by 1 thousands - for that you would use some really fine sandpaper then follow-up with the rubbing compound. Be real careful doing this as if you don't sand it down in a way that is concentric, it will give you non-concentric necks.

 

[bigedp51]

If you want to crimp "CORRECTLY" RCBS makes AR series dies with a "TAPER" crimp, do "NOT" roll crimp your ammo, the taper crimp is more forgiving on case length variations and "LESS" crimp is required.

And BoydAllen said you were making this too complicated.
(do any of you remember the TV commercials "When E.F. Hutton talks, people listen!")

Below, whats wrong with being .001 smaller in diameter for .223/5.56 AR15 ammo to prevent the bullets from moving.

Below is from Sierras Exterior Ballistics, and is in the front of the Sierra reloading manual, which too many people fail to read.

Reloading for Semi-Autos and Service Rifles

Neck Tension

When we stop to consider the vigorous (read, downright violent) chambering cycle a loaded round endures in a Service Rifle, it becomes pretty clear it suffers abuse that would never happen in a bolt-action. This is simply the nature of the beast. It needs to be dealt with since there is no way around it.

There are two distinctly different forces that need to be considered: those that force the bullet deeper into the case, and those that pull it out of the case. When the round is stripped from the magazine and launched up the feed ramp, any resistance encountered by the bullet risks having it set back deeper into the case. Due to the abrupt stop the cartridge makes when the shoulder slams to a halt against the chamber, inertia dictates that the bullet will continue to move forward. This is exactly the same principle a kinetic bullet puller operates on, and it works within a chamber as well. Some years ago, we decided to examine this phenomenon more closely. During tests here at Sierra’s range, we chambered a variety of factory Match ammunition in an AR-15 rifle. This ammunition was from one of the most popular brands in use today, loaded with Sierra’s 69 grain MatchKing bullet. To conduct the test, we chambered individual rounds by inserting them into the magazines and manually releasing the bolt. We then repeated the tests by loading two rounds into the magazine, chambering and firing the first, and then extracting and measuring the second round. This eliminated any potential variation caused by the difference between a bolt that had been released from an open position (first round in the magazine) and those subsequent rounds that were chambered by the normal semi-automatic operation of the rifle. Measuring the rounds before chambering and then re-measuring after they were carefully extracted resulted in an average increase of three thousandths (0.003") of forward bullet movement. Some individual rounds showed up to seven thousandths (0.007") movement. Please bear in mind that these results were with factory ammunition, normally having a higher bullet pull than handloaded ammunition.

To counteract this tendency, the semi-auto shooter is left with basically two options: applying a crimp or increasing neck tension. The first option, crimping, brings up some other issues that can be troublesome. In general, crimping degrades accuracy. Most match bullets are not cannelured (which also seriously damages accuracy potential), a requirement for correct application of most crimps. Still, there are taper crimp dies available from most of the major manufacturers. Lee offers their “Factory Crimp” die as an alternative, which seems to be one of the better options for those bullets without a cannelure. That having been said, crimping is still, at best, an occasionally necessary evil. Avoid it if at all possible.

http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm

 

[stool]

dont

Need to crimp the bullets. Always a good idea to crimp bullets in any semi-auto rifle. I always full size the brass and roll crimp the bullets in the ammo for my 5.56 and 6.8 SPC AR-15 rifles

 

[stool]

you have two problems...neck damage and neck tension.
go to what was said about polishing down the expander ball

it that does not work go with a bushing dia and no expander....
fix the neck damage first..i already posted steps to do that...

silly to work on neck tension while you still have a neck damage issue