Loads below published velocities?

[Daryll]

I've been doing some load development for my new Mossberg MVP Varmint in .223, with 24'' barrel.

Using GGG Brass, Sierra 69gn Matchkings, CCi 400 primers and Ramshot TAC powder I found the most accurate load was 23.6gn of TAC.

The Ramshot data for TAC with that bullet is min 21.9gn @ 2671fps, upto 24.3gn @ 2921fps, again, with a 24'' barrel.

Last weekend I borrowed the club Chrono and tried 10 shots of the 23.6 gn load and 5 shots of the next most accurate load, 24.2gn.

The 23.6 load averaged 2650, the 24.2gn load averaged about 2750..... so about 150-200fps below the published data.

So what would cause that..? I can understand how variances in loading could increase pressures, and velocities, but why are they low..?

TIA

Daryll.

[dromia]

No two guns. pressure barrels, loads, conditions are exactly the same.

Was the OAL the same as the test loads?

Variance from actual to published is usual.

[Daryll]

Yes, seated to 2.260, as per the data.

So can I safely increase the loads to get the required velocity..? I'm hoping these loads will be good out to 600 yds, so i'd like a decent speed...

[dromia]

I would not increase the loads beyond the published maximum unless you have access to a way of pressure testing your rounds.

Velocity is not pressure, it is used as a proxy sometimes but it is a poor one especially if you are exceeding published data.

It is pressure that blows up guns not velocity.

[Daryll]

Ok, thanks Dromia,

I could go a bit higher, as the rifle is chambered in 5.56, which Ramshot give higher loads for (22.9 to 25.4gn), so i could go a grain or 2 higher... but 23.6 is very accurate, so i won't mess with it.

Daryll.

[kennyc]

Ok, thanks Dromia,

I could go a bit higher, as the rifle is chambered in 5.56, which Ramshot give higher loads for (22.9 to 25.4gn), so i could go a grain or 2 higher... but 23.6 is very accurate, so i won't mess with it.

Daryll.

for target use accuracy is everything, even velocity isn't as big a deal (assuming you have enough umph to get to the target and give you the accuracy)no need to chase the last 100fps unless its effecting your accuracy, and a blown up action rarely wins matches
don't get dragged down the road of chasing extremely high speed, and always look at the test barrel length on the printed load data, its often several inches longer than you are expecting, and of course as Dromia has pointed out there are lots of enviromental differences to consider (including constructive interpretation of the results to give that market leading velocity )

[channel12]

Don't forget that temperature will affect velocity. If you chronographed your rounds in cold weather and the test data was done in an American summer there will be a difference in recoreded velocities

[Daryll]

Thanks for the comments Gents.... I'm not that fussed about the velocity, as Kenny said, as long as they reach and penetrate the target accurately!!

But I was curious why my velocities are so low.... I've looked at some commercial .223 ammo, and they're all quoting 2800 - 2900fps for a 69gn bullet.. which should be about the same for the TAC loads..
I could understand some variance... 50-100 fps... but nearly 200 fps?? And my MVP is the same barrel length as the quoted loads..

Stange... maybe I'll buy some factory ammo with a quoted MV, and chrono that with mine ammo...

[rox]

I could understand some variance... 50-100 fps... but nearly 200 fps?? And my MVP is the same barrel length as the quoted loads..

Bore/Groove dimensions?

[Mattnall]

People often get too fussy about velocity.

If you didn't use the chrono you would have been happy with your rounds and their accuracy, blissfully ignorant of their leisurely stroll down range.

Now you're worrying about something that didn't matter before.

Unless you need to go further and faster, let it go.