OAL vs. Bullet Free Travel (jump) in AR15

[plodder]

Bushmaster 5.56 with 20" 1/9 barrel.

I cannot come near the recommended bullet free travel (jump) dimensions (reported as .020" to .040" for "hunting & plinking")

Reasons for this:

#1: To have any bite or crimp on 40g. Hornady Vmax I must seat to 2.175". With the measured 2.375" OAL of this combination, that leaves .200" free travel.

#2: Of my 3 magazines, none will accomodate an OAL of more than 2.300". Since I purchased a semi-auto, not a single shot, and I would like to retain that capability; how am I to accomodate some combinations that have a loaded OAL of up to 2.565"?

Does anybody really pay attention to OAL with the typical range/fun shooter AR15?

 

[wanderinwalker]

To retain your semi-auto, magazine-fed capability, you're just going to have to seat the bullets to fit the mags and let jump be what it will be.

I load and shoot quite a bit of .223 for NRA Highpower for my AR-15. I've never loaded a "magazine" length bullet anywhere near the rifling. A Sierra or Nosler match bullet seated at 2.26" OAL is about the best you're going to do. I've never played with the sub-50gr bullets in .223, but I do use 52gr Noslers from time to time and seat them shorter to get enough bullet into the case neck. They shoot fine for me this way.

Now, to accomodate your loaded rounds "up to 2.565 inches", you just single-load them into the chamber. Bullets that have to go this long in a .223 are generally the 75-90gr VLD type bullets, and long-range/Highpower shooters use them in single-shot mode only. Again, I've loaded bunches of Nosler 80gr bullets for 600-yd shooting, trying to keep them .020" from the lands. There has never been a chance of these going into any of the magazines I have.

 

[gamestalker]

A couple of things here. Load so that they will fit the mag. and feed properely. And regarding the crimp and canelure preventing a more desired OAL, don't crimp those cases, it isn't necessary unless your loading for a tubular magazine. I would bet that by not crimping you'll be able to get them quite close to the lands while still fitting the mag. at less than the 2.300" limitation.

 

[steve4102]

As stated above, seat to fit the mag and ignore the "Jump". Seating up close to the lands does not always improve accuracy, it can, but it is not always the case.
Here is a little test done by Barnes bullets. Note there is more than one OAL sweet spot, one up close and one far away. Scroll down to "From the Lab".

http://www.barnesbullets.com/resources/newsletters/september-2007-barnes-bullet-n/

 

[Slamfire]

The 69 and 75 grain match bullets are jump insensitive. With your twist the heaviest bullet is going to be a 69.

Bullet jump is a concern for those loading 80's at 500 and 600 yards, and I remember guys using Berger bullets at long range. They were shooting HM scores, were bubbling about the great Berger bullets. But the next time I saw these guys, no Berger bullets. The reason was the throat wore and Berger bullets were jump sensitive. They could not predict just when accuracy was able to crash, and driving a couple of hours, spending $30.00 in gas and $25.00 in match fees, pulling targets all day, only to have your bullets ruin your score, well they went back to jump insensitive bullets.

 

[rcmodel]

Hornady recommends 2.200" OAL with that bullet.
Your Bushmaster more then likely has a 5.56 NATO chamber?

Anyway, there is no way possible you can load to the leade with that light a bullet.
Or probably any other bullet weight that will fit in the magazine.

So, don't even try.

rc

 

[plodder]

Thanks all! Good info.