Load Data Question

[Rumple]

After loading close to max load, 22.2gr with S265 (max as per somchem 22.5gr) my 7.62x39 bullets are accurate-ish (but not accurate enough). They travel at 2201 fps vs the factory loads at 2357 fps (they are very accurate), bearing in mind that the load data from somchem is for a 125gr bullet (mine is 123gr) and their test barrel was 22" and mine is 16.3".

My question is would another 156 fps make a difference? 

Somchem Data

BARREL LENGTH    POWDER    CASE    PRIMER    BULLET grains                COL mm
 22"                                S265    PMP    PMP      125gr Speer SP                55.1 
   
LOAD TYPE    LOAD    grain  VELOCITY ft/s    V/C factor
         
            Start              20.3      2 196            108.2
              Max              22.5      2 373            105.5

[Ds J]

The bullet speed might make the difference. A very experienced gun smith once told me that most of the accurate loads are within the first grain over minimum, and within the last grain before maximum.

The factory ammunition is most probably reloaded with a completely different powder, which also makes a large difference.

[Tripodmvr]

Your barrel is much shorter than the Somchem test barrel, so your speed would be down by 150 to 200fps. Some factory ammo is loaded quite heavily. I would not shoot that action at level continously. Have a look at my calculation and to be close to Node 7 a charge of 21,6gr is calculated.. Your coated bullets might be part of the poor precision of the ammo.

[Rumple]

Your barrel is much shorter than the Somchem test barrel, so your speed would be down by 150 to 200fps. Some factory ammo is loaded quite heavily. I would not shoot that action at level continously. Have a look at my calculation and to be close to Node 7 a charge of 21,6gr is calculated.. Your coated bullets might be part of the poor precision of the ammo.

Those were Winchester 7.62X39mm, 123 gr PP.

[zguy]

Those winchester bullets, are they meant for .308 or 7.62x51 ?

Do you know the actual diameter of those bullets?

[Rumple]

Those winchester bullets, are they meant for .308 or 7.62x51 ?

Do you know the actual diameter of those bullets?

The packet says 7.62x39 .310 and they measure .310...the neck is resized to .308 so the neck tension is .002, I factory crimp them on the cannelure. I'm going to try some new starline brass...all the brass I use I check with a lyman case gauge that measures the case length and shoulder bump... As soon as I can get my hands on some CFE - BLK I'll give that a try.

Edit- Just looked on the Winchester website, those bullets have been discontinued...the description on the product code says..." Winchester Ammo WB762PP123 Centerfire Rifle 7.62mm .310 123 GR Power-Point 100 - Bullets are custom designed and manufactured to precise specifications to deliver specific on target performance characteristics. These power point bullets feature positive functioning, good accuracy, no expansion and no barrel leading"

On the product description from the shop I bought them it says "Winchester 7.62X39, 123GR PP, Bullets [100]"

[Rumple]

Ran the bullets at max load on the 123 gr and 150 gr...seems more like a group  Noob question do you zero your rifle for different bullets?

[Ds J]

Military ammunition is usually one bullet weight at one given speed, hence zeroing a rifle is not very necessary, except to zero the rifle to the general load.

Generally speaking, as soon as the bullet weight or shape changes, the rifle needs to be zeroed.