7.62 NATO Question

[riverats]

First-time 7.62 x 51 reloader here & I am questioning my choice of projectiles, X-Treme 147gr. FMJs, which are noteably shorter than both the Hornady & IMI (150gr) FMJ-BTs pictured below.

My concern centers on the amount of purchase shared between the X-Treme projectiles, which have a slight radius @ the base, & the once-fired IMI case necks.

Reload Specs:
Case - 2.005”
C.O.A.L - 2.795”
SW Tactical Rifle - 42grs @ 2710 fps
Winchester - LRP
Medium Crimp (Lee FCD)

Are my concerns justified?

L-R: X-Treme, Hornady, IMI


Left, 147gr reload
Right, Factory IMI 150gr 7.62 NATO

 

[Another_Kelley]

If it were me, I'd just seat that baby closer to the cannelure, and see how they shoot... assuming you aren't going to be extra compressed. Looks like they're pretty differen't bullets, so no need to be at the exact same over all length as the factory loads.

 

[riverats]

…seat that baby closer to the cannelure…

Thanks, A_K…

I avoided that because of using 308 data on 7.62N cases … but, seeing where the IMI bullet (base) resides, I could go with a lower C.O.A.L. without creating pressure issues.

Hmmm, but how much bullet jump is too much??

 

[NuclearMeltdown]

How much is too much? A question for the ages!

Conventional wisdom says to seat as close to the lands as possible, but generalizations have so many exceptions in reloading that the only way to find out is to try your current length and the length when you seat to the cannelure like Another Kelley suggested.

I'd try ten rounds of each and see if your group size changes.

 

[FROGO207]

If you work up the load partially with the shorter bullet inserted more there should be no problems. And observing bullet shape the ogive of the shorter bullet will be hitting the lands from about the same spot if both were to be inserted to the canalure. I have run into this before. Overall length of a projectile is not an end all be all set in stone amount. It is what that particular bullet in that particular barrel worked like.

Also from personal shooting for years any neck crimping of my ammo does reduce accuracy in my guns. At some point try some crimped and some uncrimped then decide what you like best.

 

[Atavar]

I must agree with what others have said. The critical measurement is ogive to the lands, not COAL to the tip.
COAL is just a quick and easy approximation toward that.
If you seat those to the same COAL you are actually moving the ogive way forward.
Seat to the cannalure.

 

[Atavar]

If you want to do an interesting experiment get some 1/4” or smaller washers and drill the center hole out with a 19/32” or “N” size drill bit.
This will make the inside diameter of the washer roughly equivalent to the inside diameter of the lands in your 7.62 barrel.
Drop the drilled washers on to the tip of your loaded rounds.
The position the washers sit at on the bullet will show you where the bullet will first contact the lands.
If you do this please post a picture comparing your bullets to factory.

 

[MonkTx]

The hornady FMJ is probably the most accurate FMJ you'll find and it tolerates the huge jump well if seated to the cannelure.

 

[DMW1116]

The hornady FMJ is probably the most accurate FMJ you'll find and it tolerates the huge jump well if seated to the cannelure.

Can’t argue with that. Responded to sub the thread. I have a good stick of Hornady 308 FMJ but may try some pulled bullets when they’re gone. They could probably look like any of these three.

 

[AJC1]

Based on your pictures if I could pick a bullet the imi looks the best. The lower section of the bearing surface appears to be above the neck shoulder junction. For a semi where you want to crimp the cannalure would be in a good place. I don't crimp unless I need to, and I develop enough neck tension in the 6x45 and 233 semis I load.

 

[rdnktrkr]

I've always tried to get close to the lands or load to magazine length for max OAL, then when reading around I ran across an article about bullet jump and they are at .050-.090, something I was always taught to avoid, I've tested bullet jump with a couple of my rifles and never went above .020. In a semi I agree in a little crimp, but little is better. Test each new bullet for its OAL by putting one in a case and push the case into the chamber, you will find different bullet designs have different OALs.

Bullet Jump Research

shortactioncustoms.com

 

[Slamfire]

If you are shooting these in a gas gun, don't attempt to seat to a max distance. You want clearance between the bullet and magazine. Long rounds have a history of jamming in the magazine, I loaded my 150's and 155's to 2.750" for gas guns and bolt guns. Stripper clip loading bolt guns in rapid rifle NRA across the course, I did not want long rounds that would catch on the front edge of the magazine box, nor wedge inside the box. And that happened to, funnies happen. My ammunition would shoot cleans at 300 yards. For those who only shoot single shot and off bags, function is not as important as shooting against the clock with an unsupported rifle.

The load you picked is a good one, it is nice mid pressure load, and as such, you won't be blowing primers because of small seating variations. Seat to the cannulure and forget OAL.

 

[Charlie98]

The load you picked is a good one, it is nice mid pressure load, and as such, you won't be blowing primers because of small seating variations. Seat to the cannulure and forget OAL.

I would tend to agree... except for the Hornady bullet. It's my understanding the Hornady bullet was intended for the M1 Garand, hence the high cannelure. I just seat those bullets to 2.780" (in the 7.62mm), ignoring the cannelure, and call it a day. Over the years, using different brand bullets (in both 7.62mm and 5.56mm...) with different geometry, I just seat the bullet to the same general base depth... to keep the pressures relatively consistent.

I also agree with the comments about no crimp, even with autoloader cartridges. It took me a... LOOOOONNNNG... time to trust not crimping semi-auto cartridges, but with a little bit of testing, and some therapy, I'm past all that. Neck tension is the key.

As far as bullet jump, you will just have to test a few rounds in your particular rifle(s) and see what shakes out. Remember that FMJ bullets are not the most accurate bullets on the planet, so don't expect SMK accuracy from mass produced FMJ bullets... jump or no jump... although I will agree the Hornady is a good bullet. I'm not familiar with the other two, so I can't comment on that.

 

[derek45]

Load them to the cannelure

they are FMJ, not match bullets ?

What are you shooting them in ?

 

[zeke]

Load them to the cannelure

they are FMJ, not match bullets ?

What are you shooting them in ?

Pretty key item here, what are you shooting them in? If loading for a semi, might consider some trial dummy rounds to load from lock back and see if anything happens to col. A lot of the older surplus rounds had sealer to help keep them in place. I tried this once when loading for my FAL's, and found the bullets were actualling pulling out from the loading process. I adjusted. In a bolt or a semi, if your case neck tension is adequate, would not worry as much where the cannelure is so long as round functioned.

 

[riverats]

they are FMJ, not match bullets ?

What are you shooting them in ?

I should have answered those queries in my opening post.

The projectiles are not match, rather, they're just odd ball 147gr FMJs that will be fired via an M14SA (LRB). I have no plans of straying too far away from 147-150gr M80 ballistics

 

[Charlie98]

they're just odd ball 147gr FMJs that will be fired via an M14SA (LRB). I have no plans of straying too far away from 147-150gr M80 ballistics

Then you will be fine... that's what I load the bulk of my 145-150grn FMJ's for... not an LRB, just a Socom16. What barrel do you have on your action? If it's a generic barrel, I don't see any problems with your COL, but I understand some match barrels can be picky about it... but that doesn't sound like the case with yours.