Gunsmithing Extreme spread ?

[Jack Daniel]

Was wondering what could cause 60 fps spread in velocity in my 24" 223 using 2520 and 69smk's weight sorted brass and 7.5 primers. RRA A-4 varmint. Shoots in the 3's at 100 so I thought it would be awesome. But even I know this will cause some stupid vertical at ranges. Please advise. Thanks in advance. JD

 

[GasLight]

you know the chrony is good?

 

[Jack Daniel]

I don't? What do ya recommend. Well wait, the rifle that chad at long rifles built is single digit spread for five rounds. In fact 6fps to be exact. A few other great shooters r single digit spreaders too? It is a chrony brand? Do they suck. What do uthink?

 

[B3dlam]

How are you measuring your powder? I would be looking at this as a problem with your reloading before suspecting the gun so I would look to eliminate all discrepancies in loading first.

 

[Jack Daniel]

Chargemaster, very careful, calibrated,

 

[GasLight]

I would recommend shooting it out at distance, and see if you are indeed getting stringing. Can you set up the chronograph at distance, and shoot through it out there?

Is this a consistant thing, or just a 1 time deal? so many variables

have you tried the Long Rifles build at the same time?

 

[jonaddis84]

Its an AR.....

Also you can have the most consistent brass you want, most consistent powder charge, but if its just not a good combination of powder charge, seating depth, primer type you can end up with big spreads even if it shoots great at 100.

 

[Jack Daniel]

Hmm. All good points. Will keep messing. I never really played with ar's much, is this just the nature of the black gun? No body bashed my 2520? Thought y'all might? Ok, thanks,jd

 

[goosendmax]

It's an AR..... nuff said. That's why you are getting the spread. It is not going to measure the exact same amount of gas every single time to send down the gas tube or piston to cycle the bolt. There will be a little difference every time. In my tests there has been as much as a 100-106 fps. At distances up to 500 yards I have not noticed any issues in accuracy or POI. Test some factory ammo, same results. The best powder I have found is Alliant AR- Comp. And don't forget, AR's like a little crimp, at least mine does, helps the pressure build a little bit and keeps my speeds within 10 fps.

 

[Kells81]

+1 on the AR theory...

 

[Silverbullet2]

Try a different primer. I have had good luck with Remington #7 1/2's. Also, CCI's in AR platforms. J

 

[LRI]

Laboratory grade electronic balances start around $1500.00

Laboratory grade gravity is free.

Good luck.

C.

 

[bodywerks]

Besides the AR being a factor, you could have equal charges down to the granule accurate and still have spreads nearing what you are seeing. Really, for the average, precision minded non benchrest shooter, ES in the mid teens to low 20's is acceptable. Eliminating variables like case capacity, amount of tension on the bullet, amount of bearing surface of each bullet, weight of each bullet, primer pocket uniformity, primer quality (match verses non, brand), primer seating depth, concentricity of the loaded round, oal to ogive for each round, etc. all need to be consistent to achieve consistent single digit spreads. And i didn't even get into the rifle variables either! The biggie would be the quality of the gunsmith that chambered and finished the match barrel. And don't ever expect consistent single digit results from non match, factory barrels.

Sent from my DROID BIONIC using Tapatalk 2

 

[CoryT]

ES is practically meaningless. If you want to look at the consistency of a load, you should be looking at SD (standard deiviation) and at a MINUMUM of 20 rounds. NO ONE has single digit SD's that are 'realistic'. No chronograph that you can buy commercially has accuracy or precision to single digits in the first place, besides any setup errors. A good quality unit, like the PVM-21, is accurate to < 1% of the actual velocity, perhaps as good as .5% if care is taken to shoot perfectly square through the sensors. Now normally that error will be fairly consistent from shot-to-shot in a given string, but even small changes in the position of the bullet going through the screens will create some error.

I load things like the .338LM and .375CT for use at 1500m to 2500m. What I'm looking for is the smallest SD I can get over at least a 20 round string. While the PVM might report that as 9fps, I can be reasonably sure that's not only not the ACTUAL value, but that it only represents the value for THOSE shots anyway. What it DOES tell me is that this load is as consistent as it's possible for me to measure, which is all I can do in the loading process.

At an SD of 9fps, it's entirely possible to see an ES value of 54fps during any given string of fire, it's just not very likely. It's possible in this case that your 60fps ES reading is a load with a SD of 20 and needs work, or an SD of 10 with 1 outlier in the string. Without knowing how many shots are in the tested string and all the velocities, there is not enough info to form any valid conclusion.

 

[Sonic Crack]

im not familiar with 2520, is it temp stable?

 

[WhiteHorze]

If you've got it down to 60FPS extreme spread your doing alot of things right.

Next step: neck turning.

Your neck tension is more sensitive with the smaller calibers.

You can pick up a used drill press for $30 bucks and mount up a collet prett easily.