Range Report: RB No. 5 7mm Spanish Mauser

[FatJackDurham]

I snuck out of work early today so that I could get down to the range and test the 7mm Rolling Block No. 5. I had ordered some lead bullets, but they were too long to fit the throat, so I ordered some jacketed .287 bullets from Buffalo Arms. The bore groove diameter is .287, so I am reluctant to use the .284 standard bullet. However, in every case the loads were much higher velocity than the Lyman load manual said. I would be interested to know what you think the reason is. If the bullet is a little too wide for the bore, would that lead to higher pressure and therefore higher velocity?

I had a LOT of copper fouling during clean out. Bright, bright blue patches were coming out after soaking the bore with solvent. Maybe it would be better to use the .284. I have three left, so I can try it.


Here is the rifle. Now that I know it shoots well, I need to figure out how to blend the forend stocks so that it matches the buttstock. I ordered replacement, authentic forends from Ken Womack to keep the gun as authentic as possible.


During the original test, I had a 2 foot group at 50 yards. The muzzle ran out to .291 with no rifling, so I trimmed a half inch off and hand crowned it with the Brownells 11 degree crown.


All loads were with IMR 4350 powder, 42.3 grains up through 43.7. 

Code: Select all

Bullet	      Type  Wt.  Primer  COL gr/mass  Average fps SD % /fps Group Size	 Range MOA
Buffalo Arms	JSP	154	FLR	3"	42.3	2511	35	1.39%	2.5	50	4.77
Buffalo Arms	JSP	154	FLR	3"	42.6	2556	19	0.74%	2	50	3.82
Buffalo Arms	JSP	154	FLR	3"	42.8	2525	27	1.07%	3	50	5.73
Buffalo Arms	JSP	154	FLR	3"	43.1	2562	23	0.90%	2.5	50	4.77
Buffalo Arms	JSP	154	FLR	3"	43.4	2555	10	0.39%	2	50	3.82
Buffalo Arms	JSP	154	FLR	3"	43.7	2588	17	0.66%	1.5	50	2.86

Each group was 5 shots. I didn't post the worst ones. The sun was in my eyes, I was sweating, I couldnt see. Even with all this, using military iron sights, the gun shot well.









It was so hard to get a good sight picture because the rear sight notch is just even with the receiver. I think I will maybe load up a few more and try it out at 100 yards to see if raising the sight just a little helps. In every group, I'd have three less than 1", but then two out at two inches. Also, the primer was just a little flate. There was a fellow with 7mm experience there watching and he suggested that the 2500 fps speeds meant I was pushing the higher end of the pressure range. Certainly, when compared to the Hodgdon site, and the Lyman book, that seemed true. He suggested 4895. Thoughts?

Also, when I fire formed the cases, they shrank a tad in length. Now, they have all stretched (thanks to the factory crimp). So, I wonder what had more effect: The .28 wide bullet, tight to the bore or the shorter case? Which would lead to more pressure and speed?

Another question I have is: Which leaves more fouling, a tighter copper bullet to a rough bore, or a looser copper bullet that may allow out gasses?

I think I'll load the .284 bullets I have left, and some .287 and shoot at 100 yards to see how it goes.

[earlmck]

Dang! I think you are going to have a shooter there. Congrats!

And as for that extra velocity you are getting, don't worry about it. I'll bet your pressures are very normal and the story is in that 30 inch barrel you are launching them through.

I ran your 43.1 grain load through QuickLoad to see what it predicted. Quickload thinks you'd get 2580 fps at a little less than 40K psi from that 30" barrel, while it would call for only 2450 fps from a 24" barrel, and just 2330 from a 20" barrel. That old H4350 likes nice, long barrels!

My guess is that you'll spill a little gas and so get a bit less velocity from the smaller .284 diameter bullets, everything else equal. Let us know what you actually get (I have noticed that real life data pays little attention to the "experts" and their predictions).

[GregT]

Just wondering what your expanded case neck looks like? Can you almost insert a .308" caliber slug before you resize it?
GregT

[FatJackDurham]

Yeah, i dont have a 308. But, yeah, i can ring the .284 like a bell in the case mouth

[Marc]

I would stay with 4350. 4350 is a well behaved powder in cases like that. It is the first powder I try in my 1895 Winchesters in both 30-40 and 30-03.

I doubt that the larger bullet is causing high pressure. Ackley proved that isn't the case. A rough throat can cause it. I agree with Earl that it is the longer barrel that is giving the higher velocity. You may be able to get decent accuracy with the .284" bullets too. Worth a try.

Jacket fowling is a fact of life in a rough bore. I shoot more cast bullets in my old timers to avoid it. A steady diet of wheel weight bullets will also polish the bore. I figure if I shoot enough wheel weights I will be able to shoot jacketed with reduced fowling. Hey, it worked on a 7-30 Waters barrel for my Contender!

That rifle shoots well enough to take hunting!

[Pete44ru]

.

FWIW, I've found it best not to try to match a forend/buttstock by staining/etc one or the other.

I've always gotten a perfect match by stripping both (I haven't used sandpaper in 15 years, except on a repaired area), then staining both to a match & finishing the result.



.

[FatJackDurham]

Good advice all around. I was going to polish the chamber a little. Maybe I'll try lapping the throat to take the roughness out.

[kasTX]

Any idea what produced the crescent shaped marks on targets 3 and 4?

The last time I saw something like that, I was shooting 350gr Rainier plated bullets out of a 500 S&W. Asking around, the answer I got was that the marks were created by a piece of the plating hanging off because I was pushing them too fast (supposed to have been loaded to lead bullet velocities, around 1,000 fps).

Hard to believe a piece of jacket would hang on at 2,500 fps though.

[FatJackDurham]

I wondered that too. But if plate was hanging off, wouldn't the bullet tumble or fly off?

I thought maybe the target wasn't flush to the backing, and was dimpling in while the bullet was twisting through....

[Nath]

I am surprised H4350 is showing sign of pressure on those charges!

H4895 will pressure up quicker still!

Nice report

N.