Velocity

guncollector · Posted: Tue Apr 25, 2006 12:04 pm Post subject: Velocity

For the first time I can remember, I chronied some new loads significantly faster than the reload books said they should go. I was loading for a new 338 RUM. I was expecting 3000 fps or so with a 250gr SGK and got more like 3300! Similar results with a 210 gr Barnes TS - about 10% higher than the book says.

Shooting a Rem 700 SS 24 inch barrel. The only difference from the book loads were WLRM primers instead of Rem9.5. Seated 0.04 off the lands with the SGKs and 0.06 with the TS's.

Thought it might be the Chrony so I tried a 8mm Mauser that I have previously chronied at about book velocities and it came in right where it should.

Usually I find my results to be 5-10% slower than the load books.

Anyone have similar experiences?

Handloader · Posted: Tue Apr 25, 2006 12:28 pm Post subject: Re: Velocity

Hi guncollector: welcome to the forum. There are some fairly knowledgable folks here and I always learn something new from their contributions.

Variations from book velocities, higher or lower, are common and underscore the variables that determine bullet speed. Once I had a chronograph that changed its velocity relative to the position of the sun; when the sun got above 45 degrees from the horizon, the velocity would record 20% lower! So, you can't discount the chronograph itself and, like you, I have some standard loads available to verify readings.

Obviously different barrel lengths account for some discrepancies from book results, but, even more, different bullets of the same weight/caliber seem to make an equal difference. Hence, the recommended proceedure of using the bullet's manufacturer's data and work up judiciously.

Post SAAMI, velocities from book to range seem to be more consistent but I always pay attention to the type of firearm or universal receiver used for the tests and the barrel length.

DallanC · Site Admin Joined: Jan 18, 2005 Posts: 3572 Location: Utah

Welcome to the site Guncollector!

I keep hearing great things about trippleshocks... I havent tried them yet due to HORRIBLE experiences with XLC accuracy but I'm tempted to give TShocks a try.

How was accuracy with them? I'd like them for my 7STW which is also a fast shooting rifle.

-DallanC

roklok · Posted: Tue Apr 25, 2006 5:44 pm Post subject: Re: Velocity

I had a similar experience recently loading 45-70. Using the exact load listed in the Speer manual with same gun and barrel length (22" Marlin 1895) I was getting 200 fps faster than the manual stated.400 gr Speer in front of 52 gr reloder 7 listed at 1860fps,I was getting 2060fps.Like you I was checking other rifles and loads at same time and they were as expected so I dont doubt the readings.This was the first time I had such a wide difference in velocity.Most of my loads do about what the book says.A pleasant surprise!!

yooperchuck · Posted: Tue Apr 25, 2006 6:44 pm Post subject: Re: Velocity

While setting up my chronie I had a guy say that 7 feet was fine because that was how he set his up when they first came out. Manual said 10 feet. I went along with the guy. Just hoping i didnt shoot the chrony my first time out. Appreciated his help. Next time I went out I set up at ten feet. Per manual. Shooting some of the same rounds I got lower reading in fps. Not much but noticeable. I was told that the shockwave from my .308 at 7 feet could give higher readings. Hope ya find out whats happening. Im struggling to find a good OAl, powder charge, bullet, brass, primer combo that will give me consistant fps mostly for some longer range shooting. Or whatever my stock remington bdl .308 varmit special will allow me.

Vince · Posted: Tue Apr 25, 2006 8:08 pm Post subject: Re: Velocity

guncollector wrote:

For the first time I can remember, I chronied some new loads significantly faster than the reload books said they should go. I was loading for a new 338 RUM. I was expecting 3000 fps or so with a 250gr SGK and got more like 3300! Similar results with a 210 gr Barnes TS - about 10% higher than the book says.

Shooting a Rem 700 SS 24 inch barrel. The only difference from the book loads were WLRM primers instead of Rem9.5. Seated 0.04 off the lands with the SGKs and 0.06 with the TS's.

Thought it might be the Chrony so I tried a 8mm Mauser that I have previously chronied at about book velocities and it came in right where it should.

Usually I find my results to be 5-10% slower than the load books.

Anyone have similar experiences?

G'Day guncollector, welcome to HuntingNut. You will find a wealth of knowledge here.

The WLRM primer.....is this a magnum primer? If so, this will lift velocities. I remember reading my first reloading manual thoroughly when I first started reloading.....I needed to know what I was doing ......and I remember reading that using a magnum primer, at least when loading pistol, can be the same a increasing your load by up to 1.5 grains of powder. This could account for your extra velocity.

I would be having a very close look at the cases for excessive pressure signs. If there are none then look at your chrony. If everything seems correct there then I would look at your load and projectile position in relation to the lands. It could also be a combination of all of these things.

I would certainly be investigating thoroughly to ensure that your loads are safe.

Good luck mate.

Cheers, Vince

guncollector · Posted: Wed Apr 26, 2006 6:48 am Post subject: Re: Velocity

Thanks for the ideas. I'll let you know how it works out.

Regarding triple shocks and accuracy, I was getting <1" groups at 100 yards with the best load and std deviation was 7.5 so I'd say that was accurate. That was my first time out with this rifle so I'll be playing with it some more.

I also use X bullets and TS in my 270. In this cae, The X-bullets are more accurate than the TS's but both are 1 MOA or better. I tried XLC's and did not have any luck with them. A couple of things do seem to be consistently true with barnes bullets - drop down one weight class for the caliber if you can and seat 0.06 off the lands. In other words, most people think of 130 grain bullets for a 270 but 120 barnes bullets seem to be a bit more accurate.

In any case, not all rifles will like barnes bullets but they sure are good performers if you can make them work in your rifle.

Flint54 · Posted: Wed Apr 26, 2006 10:05 am Post subject: Re: Velocity

Welcome to the land of variables. As stated make sure that your crono is set up at the recommended distance. Once that is set start your testing but always remember that barrels will shoot diffrently. No two barrels will give the same results and yes, you may come across a barrel that shoots faster. Although 200fps is a bit on the high side so you need to check for any pressure signs. I just got a Ruger Ultralite with a 16.5" barrel in .308 Win. (A). I also have 3 other .308s. A Savage 99C with a 22" bbl (B), a Savage 10FP with a 24" E R Shaw bbl (C) & another Savage 10FP with a 26" Kreiger bbl (D).

My target load is Lapua cases, CCI LR Benchrest Primer, 155gr Nosler Custom Competition bullet, 47.5gr BL-C(2) loaded to an OAL of 2.785". This load gives me sub 0.5 MOA from the Kreiger BBL, and sub .75 MOA with the ER Shaw. With the 99 and a tang sight @ 1.5" and in the UL so far ist staying under MOA.

Here is the suprise!!

Rifle (D) 2855fps - SD 14fps
Rifle (C) 2795fps - SD 18fps
Rifle (B) 2580fps - SD 28fps
Rifle (A) 2720fps - SD 15fps

I cannot explain how or why the UL shoots as fast as it does but it is right on the heels of my 24" barrel and way above the old 99. The 99's bore is bright and clean but runs a bit over sized so it shoots a bit slower than the rest. I am going to set down in the future and do some accuracy testing with the UL and see what it can do. This will be a 3 shot group rifle as I don't expect to be using it for much other than hunting and I will say for a .308 it lets you know you shot something 8-O. With scope and sling it just goes a tad over 6.25 pounds with a full mag and empty chamber, the way I hunt with it.

So, check for pressure and if you don't observe any signs be happy with your new laser!!! Cool

shootist · Posted: Wed Apr 26, 2006 10:28 am Post subject: Re: Velocity

Hi GunCollector...

Here's my $.02....listen to VINCE

Anytime you get a 10% INCREASE from expected results...Take heed!

1. Shoot Factory 250's through the chronograph and note the results.
If 100fps over about 2900fps, back off your loading of the 250 SGK's to match the factory loadings, paying attention to OAL and crimping.

2. Keep factory loads on hand for reference measurements.

3. Check the Reloading Database here for similar loadings, since you didn't
mention powder,weight etc.

4. The maximum SAAMI pressure is 65,000psi. and factory loadings with 250gr bullets is around 3000fps. It's difficult to pinpoint, but case length,crimp,powder density,compression,fracture etc. all increase corresponding pressure.

5. Take some case web measurements.

6. Again...listen to VINCE

SHOOTIST

guncollector · Posted: Wed May 03, 2006 1:39 pm Post subject: Re: Velocity

Update -

I went back to the range and stretched out the cable connecting my chrony to the readout as far as it would go. Probably 3 or 4 feet further than the last time. And suddenly the velocities dropped down to just about what the books say they should be. I think that there was enough muzzle blast reaching the chrony the first time around to make it appear that things were moving faster than reality. When I tried that 8mm load the first time as a check, it didn't have near as much muzzle blast so it was reading correctly. Lesson learned - larger calibers with larger muzzle blast must have more distance between the muzzle and the chrony to be accurate.

shootist · Posted: Wed May 03, 2006 4:22 pm Post subject: Re: Velocity

Hi Guncollector...glad you have it solved .

Regards,

SHOOTIST

Vince · Posted: Wed May 03, 2006 7:25 pm Post subject: Re: Velocity

guncollector wrote:

Update -

I went back to the range and stretched out the cable connecting my chrony to the readout as far as it would go. Probably 3 or 4 feet further than the last time. And suddenly the velocities dropped down to just about what the books say they should be. I think that there was enough muzzle blast reaching the chrony the first time around to make it appear that things were moving faster than reality. When I tried that 8mm load the first time as a check, it didn't have near as much muzzle blast so it was reading correctly. Lesson learned - larger calibers with larger muzzle blast must have more distance between the muzzle and the chrony to be accurate.

Cheers mate. I'm glad it all worked out.

Best lesson to be learned from all of this is:

If something isn't right or if there seems to be a problem.....especially a SAFETY issue.....STOP, go back to the start point and start checking everything that could be a possible problem. Better to check everything twice and be assured that all is ok than to say, "Well, that is near enough" then go out and blow up your firearm and injure yourself or one of your mates.

Time to go out and bust some caps, put some rounds downrange. Very Happy

Cheers, Vince

Coyote_Hunter_ · Posted: Thu May 04, 2006 8:53 pm Post subject: Re: Velocity

I already shoot TSX's, although I haven't had a chance to take any game with them. Like Dallan, I had a horrible experience with the XLC's and a buck antelope suffered needlessly as a result.

Accuracy has been uotstanding, and I get around 100fps more than similar weight bullets of traditional (non-grooved) design.

So far I use:

180g, .300 Win Mag
168g, .308, .300 Win Mag
115g, .257 Roberts

Picked up a box of 140g today for the 7m Mag.

As soon as they are available, I will switch to the MRX. They will end any concerns I have about bullet expansion ( or lack thereof, as I suspect happened with the XLC's).