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Testing two rifles, identical chambers ...different barrels

 
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  #1  
Old 06-01-2006, 10:52 AM
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Testing two rifles, identical chambers ...different barrels

Both of these rifles are chambered for the 338 Snipe-Tac caliber. 338-408imp for those just reading the post for the first time.

Rifle (one) is a Stainless repeater action with a stainless
Barney Lawton barrel, 33" long twist rate 11.25 groove dia is .3295 (bbl is fluted)

<font color="blue"> </font> Rifle (Two) is a Titanium repeater action with a Mike Rock 5R bbl-ABS carbon fiber system 33" long 9.25 twist rate. Groove dia .329

<font color="green"> </font> I tested the same loads in both guns to see how much the speed changes with tighter bores.

300MK 141grns H-BMG50 powder
gun one: 3395
gun two: 3305

250MK 149.5grns WC 873 powder
gun one: 3438
gun two: 3360

<font color="black"> </font> I set up some targets at 100, 400 and 500yds to test some loads in both guns.

Gun one at 400yds with 300MK bullet WC 873 145.5grns 3400fps ave. Group 1.2"
[image][/image]

Gun two at the same range, 400yards, with a different load,
300MK 141grns H-BMG50 3305fps average. group size .352

[image][/image]

I then fired gun two at 512yards with same load, 300MK
141grns H-BMG50 powder 3305fps group size .540

[image][/image]

I shot some 350grn wildcat bullets for comparison, 141grns WC873 powder...3060fps (starting load) 100yds These shot right at 1" Didn't do much load testing as i only have about 20 left. In gun one several weeks ago the same tests were no good with the 11.25 twist. 3250fps

It appears there is about 90fps difference between the two barrels, the tighter bbl is a bit slower. It is hard to say what the accuracy difference is between both guns, the triggers are not the same, Gun Two has a Shilen trigger set nice and crisp, gun one has a factory Remington trigger and it needs work or replacement. Both guns will cut a bug hole at 100yds. Due to trigger issues with gun one, i didn't do any 500 yard testing, just pulling the trigger on the 400yd target i could see the crosshairs moving back and forth across the target before the sear would drop. I am so use to a 2 ounce trigger that a 3# pull is a nightmare!
Both of these rifles are carry hunting guns and are set up accordingly.

Both chambers are identical.
Barrel lenths are 33"... with brake, 35.5"
Both guns have the same carbon fiber Lone Wolf stocks.
gun one has a IOR 6-24 with 35mm tube
gun two has a Nightforce 5.5x22 30mm tube
both guns have a 40moa picatinny base

Gun one weighs 16.7#
Gun two weighs 15.2#

both guns shot from sandbags on my special shakey bench!
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Old 06-01-2006, 11:37 AM
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Re: Testing two rifles, identical chambers ...different barrels

From looking at the very dirty rings around your bullet at 400 yards and from the speeds you got, I would venture to say that the powders you are trying might be a tad on the slow side for your guns.

I typically do not see as dark of rings around the holes at 100 yard BR matches and your target was 4 times further out and jet black. That tells me the powder is burning dirty and/or inefficiently or it is a hot day or both.

COnsider this:
96 grains of RL25 shoots 300 grain MK's at 3075 from a 36" barrel in a 338 lapua improved over my oehler 35 on a 4' rod. You are dumping in roughly 50 more grains of powder and only getting only 225 fps more with a 3" shorter barrel. That has got to be "sandblasting" your throat with oodles of unburned powder.

This might be one of those cartridges that will shoot a slightly faster burning powder at unreal velocities. I would try VV170 or Retumbo and see if it likes them. I'd be willing to bet it shoots faster (although it may or may not shoot as good as you're getting now with H50bmg-those are great groups!) with a slightly faster pressure curve.

It might be like the 30-378 wby. The powder everyone seems to use is H50bmg and 180-200 grain bullets and they never go faster than a 300 ultra will using 20 grains less of a faster powder! Then you run RL25 or Retumbo in the 30-378 and they will shoot 180's about 3500 fps and best the ultra by 100 feet or so. The gap gets even wider when heavier bullets are used.

ANyhow, looks like a very fun project and it should keep you busy for awhile for sure! Enjoy that monster! [img]/ubbthreads/images/graemlins/cool.gif[/img]
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Old 06-01-2006, 01:01 PM
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Re: Testing two rifles, identical chambers ...different barrels

GG,

Not sure with Daves 338 but with my 338 AM I will top out in pressure before I top out the case capacity with a 300 gr pill and H-50BMG. That said, I do load up to 149.0 gr H-50BMG with my top end load. This is a 98 to 99% load density in my 338 AM.

With the 350 gr ULD RBBT, I have a significant amount of air in the case. I would say topping out at around 90% load density with H-50BMG.

I would be a bit on the nervous side to try Retumbo in my 338 AM at least with a 300 gr pill or heavier. H-50BMG seems about right for the 300 gr SMK and I am loaded up and ready to test VV 20N29 in the 300 and 350 gr loads as well here soon as I get out to the range.

I am pretty sure BD408 can go up quite a bit in powder charge and would also increase velocity some as well and get a cleaner burn out of his 338 ST.

On the dark bullet hole thing, you may be onto something but also consider that the 300 gr SMK has nearly the same meplat as most 22 and 6mm caliber match bullets. Only difference there is a whole lot more bullet diameter so there will be similiar initial paper tear from the meplat but much more paper stretching around the larger diameter bullet resulting in more paper to bullet contact. I suspect this is the reason for the larger black areas on the target more then anything.

If you look at an expansion ratio comparision, this class of 338 rounds has a lower expansion ratio then even my 7mm AM.

The only problem with case capacities this large and bullets this heavy is that things can get serious real quick. That is where the slow burning powders give a bit extra cushion in safety margin as they give you a bit more warning when your getting to the top.

Maybe Retumbo would get some more fps but I suspect it would be a bit tricky getting it to shoot consistantly well at these top end velocities. Just what I have seen with the really big 338s.

Now a 250 gr pill, I would say that would be a very practical powder choice.

Good Shooting!!

Kirby Allen(50)
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Old 06-01-2006, 03:03 PM
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Re: Testing two rifles, identical chambers ...different barrels

Goodgrouper:

The main reason for this test was to see what the difference was between both barrels. I used starting loads while fire forming the brass, for this test, it was a hot day and basicly was all that i had loaded up. I have tried faster powders, the case is too big and you will have all kinds of pressure problems. BMG50 powder seems to be one of the best for this cartridge. 141 is a starting load i use for fire forming the cases. i use 147 for my rifle, that puts it just under 3500fps with the 300MK bullet. You can go with a quicker powder with the 250gr bullets, 3700+ fps.

I tested some WC873 powder, its a bit dirtier than the BMG but shoots rather well and lower pressure. Like kirby's gun and mine, both are about the same. I used a loading of 145.5 WC873 with the 300mk, 100yd, bug hole. 400yds, 1"

Just for testing purposes, 149.5 WC873 with the 250MK, 3/8" group 100yds. 3495fps. Low pressure load, i could bump this up to 152 or more. I will test this one later.

There is a big difference between 3075 and 3450, it takes powder to make velocity. 3450 with a 300grn bullet flat out hauls butt. Bug hole groups at 100yds, 400-500yard groupings are under 1"

33" bbl burns 99% of the powder according to Quick load,
150grns of BMG50 powder. The bbl was 35" to start with, no change in velocity after cutting off 2". Kirby is getting almost the same velocity in his 40" tube over my 33" job. His larger action and bbl seems to run a bit lower pressures than my lighter carry rifle. I can get 3520, but the case life will be short. 3450 seems to be about right in my particular rifle. I have 4-5 loadings on 12 pieces of brass i have been testing with, lost none of them. Pockets still hold primers. I did however blow a few pockets working up to see where it tops out at.
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Old 06-01-2006, 05:46 PM
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Re: Testing two rifles, identical chambers ...different barrels

Are you using WC 872 I have not seen WC 873 [img]/ubbthreads/images/graemlins/confused.gif[/img]
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Old 06-01-2006, 06:21 PM
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Re: Testing two rifles, identical chambers ...different barrels

Yea its WC872, my forgetter is working overtime today. [img]/ubbthreads/images/graemlins/confused.gif[/img]
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Old 06-01-2006, 09:29 PM
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Re: Testing two rifles, identical chambers ...different barrels


[ QUOTE ]
On the dark bullet hole thing, you may be onto something but also consider that the 300 gr SMK has nearly the same meplat as most 22 and 6mm caliber match bullets. Only difference there is a whole lot more bullet diameter so there will be similiar initial paper tear from the meplat but much more paper stretching around the larger diameter bullet resulting in more paper to bullet contact. I suspect this is the reason for the larger black areas on the target more then anything.

[/ QUOTE ]

Actually, bullet diameter has nothing to do with it at all. [img]/ubbthreads/images/graemlins/shocked.gif[/img] I thought so too until I spent a day last year at a 100-200 yard NBRSA match helping score groups. I learned from a guy who has measured tens of thousands of targets that he could tell what powder each shooter was using by the amount, thickness, and color of the "ring" around the hole. He could tell when somebody was shooting 8208 a little mild, or when n133 was screaming, or when Scot was dialed in. I was then informed that some of the guys actually tailor their loads to "cheat the ring" so their groups look smaller! This was the case with the 22 ppcs and the .20 waldog variants too.

So for the last year, I have been monitoring this phenomenon in my own shooting and by golly, it works!

Some powders reverse the hot/cold thing so you have to know which ones do that or you could go the opposite direction with it.

Very interesting stuff.

I showed a picture of these holes to my scorer buddy today and he said that he had no experience judging H50bmg but that it looked too mild or shot in cool weather! On the other hand, it could be that H50bmg is one of those reverse powders and shows opposite traits. Sheesh, just when you think you've got things figured out, somebody tells you some new trick! [img]/ubbthreads/images/graemlins/crazy.gif[/img]


And you never know, Retumbo might just give a more gradual pressure curve down after a sharp peak and surprise you! I thought for sure that RL25 was going to be the powder of choice in my 338 thunder with the 250 grainers and it shocked me when RL22 was better in every regard across the board! Thanks to 7mmrhb for "forcing" me to just give RL22 a try with the 250's! I figured it would be the powder for the 225's and it worked for both! [img]/ubbthreads/images/graemlins/cool.gif[/img]
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