SPA model M25 in .35 cal

[nervoustrigger]

I recently ordered a SPA model M25 in .35 cal from an online vendor that Rob M brought to our attention in the Bargain gate.  Just figured I'd document my observations here as I go through it in the coming days or weeks.

Out of the box, all I did was run a few patches through the barrel and mount a scope to get it on paper.

It is sending the 82gr Snowpeak domes out at 830fps (126fpe).  The report makes me think it's wasting air.

Here's the first attempt with the Snowpeak domes at 50 yards.



While that's not an impressive group, given the reputation of Snowpeak pellets, I'm actually pretty optimistic about it.  Better pellets will be here soon, and it can only improve with some barrel work.

[nervoustrigger]

Regarding the excessive muzzle blast, I had to shorten the hammer spring from 3.38" long to 2.7" in order to get it down to the velocity knee.  That helped a lot..the pressure was dropping at least 15 bar per shot initially.  Shortening the spring brought it down to about 10 bar per shot (~33% air savings) so that's a welcome improvement. 

When I reinstalled the end cap, I could see there's still a smidge of spring preload (approx 1/8") so if I get inspired I may try to cobble together an internal SSG for it.

The regulator appears to be set to about 160 bar based on where the velocity begins to taper off.

Next up will be an inspection of the barrel.  If previous SPA guns are any indication, I'll have my work cut out for me.

[smythsg]

Watching...

[stroo]

Another interesting nervoustrigger thread!   

[bear air]

Following along too. How hard is it to get to the spring? I should have mine today. If not tomorrow for sure.

[nervoustrigger]

How hard is it to get to the spring?

Very easy.  Just 4 screws...2 to get the action out of the stock, then 2 more to remove the end cap.

[nervoustrigger]

Now for the barrel.  Grrrr 

As usual, SPA did an atrocious job on the crown.  This shallow angle nonsense produces a terribly irregular bevel: 


But worst of all, they continue to use a piloted bit that damages the rifling in the most critical part of the barrel.  Just shameful.


The breech end was actually pretty decent.  The leade appeared to be neatly centered on the bore but I could see a sharp step into the rifling.  That explains why it was so hard to chamber a pellet.

So it was time to head out to the shop.  I started by using a Cratex type abrasive bit to ease the transition into the rifling.

Then I set about to pour a cast lap and work the bore.  I soon discovered a tight region about 1/3 of the way from the breech end that took 2 hours of short stroking to finally get the lap through it.  Some serious friction at play here...a couple of times I touched the barrel and it was so hot that I could barely keep my hand on it. 

Then something at the muzzle...its OD is turned down a little and then threaded.  This process usually causes the end of the barrel to open up.  In this case it was only barely detectable as the lap reached the muzzle.  So while I would have preferred to go for a taper lap, I was running out of day so I decided to stop once I had achieved a uniform feel all the way to the muzzle.  Figured I can try that first to see how it fares.

So after it felt about right, I proceeded to remove the lap and clean the barrel.  Then poured a fresh lap and did a finishing pass with a lighter abrasive.


Then I took off 1/4" from the muzzle to get back behind the scored lands, and followed with a round head screw to develop a new crown.


Hopefully it will show improvement.  If nothing else, the bore sure is pretty now.

[Rob M]

following

[nervoustrigger]

The JSB and FX pellets arrived so I was anxious to give them a try in the newly massaged barrel.

The first thing I noticed was how much easier it was to chamber a pellet.  Previously I had to push the bolt forward with the ball of my hand, and there was a sudden moment where the pellet would give way to the sharp step into the rifling and the bolt would slam violently closed.  Now I can close it with a more natural push of the thumb, and I can feel the pellet swage gently into the rifling.

So on to pellet testing but after trying a few 50yd groups with the Hades and domes, I wasn't happy.  Some would land in a decent group but there were regular fliers that would land an inch or more away from the cluster.  Disappointed, it was late at night so I put the gun away. 

As I propped it up in the work room, I noticed a dull gray residue against the black anodized finish of the exit hole of the moderator.  Aha!  Looks like pellets are grazing it.  Hopefully that's the cause of the fliers. 

More to follow in a couple of days.

[avator]

As usual, great work so far Jason. I'm following just for the experience in guns other than this one. I think it will be useful in working out some of the finicky results in my Sentry guns. I have 2 of them in .25.

[nervoustrigger]

Quick update.  Didn't have time to bore out the moderator but since the long stack (8 cups) appeared to barely be clipping, I swapped to a short stack of 3 cups.

A 50yd group with the Hades measured 1.5":


The FX domes made a 1" group.  Sorry for the small caliber holes in here...I was shooting an old target paper:


May have been a coincidence but the upper cluster of 3 was with a loose hold and the bottom 2 were with a firm hold so I'll have to experiment with that.

[bear air]

My other 357 preferred the fx pellets too. That's also good because I have a few tins. I should have some time to mess with mine this week end.

[K.O.]

So, looking at the pics...  be slow twist or have my eye's been tricked by perspective..?

10/90 on the bore groove ratio, 6 narrow lands bout .002- .0025 tall..?


hmmm 140 ish psi a 100+ fpe shot... makes my want one... as a hand pumpable hunter...

wonder how a .35 sniper med would do..

[Blowpipe Sam]

Subscribing.

[Rob M]

So, looking at the pics...  be slow twist or have my eye's been tricked by perspective..?

10/90 on the bore groove ratio, 6 narrow lands bout .002- .0025 tall..?




hmmm 140 ish psi a 100+ fpe shot... makes my want one... as a hand pumpable hunter...

wonder how a .35 sniper med would do..

i think thats 140 bar, not 140 psi

[nervoustrigger]

Kirby, yeah the rifling is pretty shallow.  Regarding the twist rate, I have no idea why I didn’t measure it while I was lapping the bore.  I’ll do that the next time I pull the barrel.  I was planning to slug it anyway. 

[K.O.]

So, looking at the pics...  be slow twist or have my eye's been tricked by perspective..?

10/90 on the bore groove ratio, 6 narrow lands bout .002- .0025 tall..?




hmmm 140 ish psi a 100+ fpe shot... makes my want one... as a hand pumpable hunter...

wonder how a .35 sniper med would do..

i think thats 140 bar, not 140 psi

from reply #1 "10 bar per shot" ... that is with about a 3500-3600 psi fill and 22.7" barrel..

[nervoustrigger]

BTW that would mean the efficiency is a lackluster 0.85fpe/ci if SPA’s claimed capacity is correct at 245cc (15ci).  They may be including the plenum tube in that figure though.  I don’t want to degas and disassemble at this point to check but I can probably run a sanity check calculation based on the external dimensions to see.  Granted with 10 shots per fill, that’s probably about 7 more than necessary for any hunt I’ll be carrying it on.
 

[Rob M]

So, looking at the pics...  be slow twist or have my eye's been tricked by perspective..?

10/90 on the bore groove ratio, 6 narrow lands bout .002- .0025 tall..?




hmmm 140 ish psi a 100+ fpe shot... makes my want one... as a hand pumpable hunter...

wonder how a .35 sniper med would do..

i think thats 140 bar, not 140 psi

from reply #1 "10 bar per shot" ... that is with about a 3500-3600 psi fill and 22.7" barrel..

ok understood now , I wonder how big the res is, thats pretty good for a big bore

[sculbert1]

I believe the barrel on my 30 is worse than your 35  :😥 😒 😑