SPA model M25 in .35 cal

[Keesbo]

Couldn't the bolt be tapped so a heavier more stout bolt could be used? That was something I was considering later down the road.

Perhaps, but I think my solution is better.

[bear air]

Tore mine down yesterday and cleaned up the hammer and area. I also did some polishing and finished my work on the barrel. Hopefully the weather is decent this next week and I can get some shooting in.

[bear air]

I put a vector optics Veyron fixed 10 x on mine the other night and took it out yesterday morning. After getting it sighted in the trigger sear wouldn't catch. I was quite miffed but figured it was probably something I did or didn't do right reassembling it. I was correct with my presumption. I took the trigger group back off last night and got it working again. Maybe give it another go this morning.

[bear air]

So here are some pictures of how it was shooting the fx hybrid slugs yesterday.

[Keesbo]

What was the distance of that?

[bear air]

Sorry, it was 50 yards. I honestly wouldn't mind getting it out to 75+. That would be more realistic shooting coyotes. But for now I need to start somewhere.

[Fado71]

Happy New Year to everyone!

I am new here as a member but have been lurking for a while and reading all i can about the M25 as there isnt much on the net about tuning the .35.

After getting mine i then found the hammer spring had no adjustment, with everything i read i never found that out until after buying but i dont think will be a big issue so very glad to see some info on the hammer spring here. I also think my report is too loud, as in shooting excess air.

I stripped mine down after having some issues with sighting it in, lots of fliers at 50 yrds and with hand pumping i wasnt sure if it was me or the gun, Last air guns i shot were springers and in my teens, now the other side of 50..... time to buy a shoebox compressor!


I found some marks on the moderator so i also think mine was clipping, now down to 4 sections on the moderator.

The air fill O ring leaked on first fill.

I found the plenum valve spring cup loose, so now i have wound it down tight, about 8 turns,  but still feels like it could rotate and move under use, thinking of adding some blue loctite to the threads?

I have polished the hammer and the spring ends that were very rough.

Removed and checked the discs inside reg, cleaned and reassembled without any reg adjustment.

I also have tightened the bolt grub screw a little that holds it when loaded, but it is still lifting the bolt a little with each shot.... that bugs me and would like to stop this.

As it seemed loud and i was finding it hard to get a decent grouping i bought a chrono so i know roughly where the reg is set at... Looking at when my fps starts to drop i think mine is set around 120-150.
Getting around 820fps with the Snowpeak domed 81grain pellets.... seems a little low to me.

I took the barrel off to inspect but think i need to look again after reading this post and check it more closely, I have some rainy days coming here so a day in my workshop is needed, so again very happy to find this thread!

I have read and saved some good articles on tuning to the knee but after finding no hammer spring adjustment i had to think of a way round it, so after reading Nervoustrigger's post about the spring work he has done i am happy to know he had removed some with good results.

Now here is a question/ An idea i would love some feedback on.....

Before seeing this thread i thought to drill out the center of the hammer spring cap and tap/thread it for a bolt, fitted so the head of the bolt would be inside the cap where the spring sits and the threaded part of the bolt sticking out, cut a grove so i can adjust it, the head of the bolt would sit against the spring.
Then i thought, if i had to, i could drill out a little from the hammer, again where spring sits inside the cup, to allow for the thickness of the bolt head, would shave the bolt head down a little, so the spring would not be under any extra tension from the bolt head.
Now after reading Nervoustrigger's post of him removing some of the hammer spring i think my idea might work, and even better without removing anything from the hammer and just removing some of the spring so i can fit an 'adjuster'....... does my idea sound ok?

I dont want to tune this thing super crazy just for good reliable accuracy.
I am thinking about to start using 120-140 grain slugs as i have a huge wild boar problem on my farm, although with the distances i would be shooting at i think these domed pellets are good enough... 60yrds max.

I shall take some photos of my barrel in the next day or so and post them here for comparison.

Looking forward to this thread growing.

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.

[Fado71]

My barrel ... from factory, thinking it has already been crowned

I have started my own post about my gun and barrel but wanted to just add my pics here for reference.

Nervoustrigger, did you cut your crown down because of your lands ?, you can see mine has some marks too and wanted to ask if there is a way to improve or fix it without cutting. (off to read your barrel troubleshooting guide, again!)

Looking forward to seeing what you do, thanks for this post, following with great interest.

[nervoustrigger]

Yes you really want to cut it back to completely remove the smeared lands.  I have fixed quite a few barrels this way.  As with most things, it’s no guarantee but most barrels respond with a dramatic improvement in accuracy.

[Fado71]

Yes you really want to cut it back to completely remove the smeared lands.  I have fixed quite a few barrels this way.  As with most things, it’s no guarantee but most barrels respond with a dramatic improvement in accuracy.

Thanks for the reply Nervoustrigger, was kind of hoping you might reply as you clearly know your stuff!
I owned a garage most of my life before moving from the UK to Spain so know my way around tools and metal and know enough that i need to do something with this barrel but out here i doubt i can find some one to turn me some new threads for the AS and mod, not on a barrel anyway. we have gun shops etc but they dont have people to do this without sending it away.... too many weeks and months , tomorrows go by, it's Spain, Amanha !!

I have been reading your great posts, 'barrel troubleshooting' etc, awesome stuff, thanks mate!... I can do it no problem but it is the threads, or 'lack of' after cutting off/ part/ all, that worries me for the AS?

I realise the choke if it has one? and the crown are the parts that dictate accuracy and consistency.
..Going to take some better pics tomorrow and stick on my post.

I would be very grateful if you can pass your eye at the new pics, unless that is the only way, to cut the barrel beyond all damage on the lands, more than the threads.
do you think i could 'try'.. say, cut 'some off', if the cut would remove around 70% of damage and polish it etc to 'help' ,obviously 'proof is in the pudding' but is it worth a try? with such little quality lathe work close by.. so as to keep the threads or most of them?
Im fully aware it isn't the right thing to do but with lack of someone local where i am that i could trust to cut the threads without ruining the end of the barrel  even more and making it pointless... BUT i hope after a good clean and some better pics i might be able to see\measure how far the damage goes and keep enough threads to hold the AS securely.
( would need to cut the AS threads and the barrel shroud down for what material is removed from the muzzle when cut so the AS holes sit at the correct level for the muzzle tip and BS is snug)


Either way thanks for all your posts and info you have shared!

[190mech]

If you have access to a lathe, could it be counter bored to remove the bad area and retain the threads?

[Fado71]

If you have access to a lathe, could it be counter bored to remove the bad area and retain the threads?

Around me here there are no good places with a lathe that can do it. I have a large lathe but is for wood, will be ok for some polishing etc but not accurate work with metal.

[Fado71]

Hi Jason,
Just wondering if you had any luck with any further work?
Mine has improved greatly in accuracy, so thanks for your help along the way.

Sorry to start this old thread up again.

[nervoustrigger]

Hi Alex, thanks for checking in.  Unfortunately I haven’t had much shop time in months but am hoping to get the M25 back out this winter.  Will definitely post an update when I do.  Meanwhile I was delighted to see your success with the hogs that you wrote up in the other thread. 

[Fado71]

Hi Jason,
So it isnt just me without enough time then
I will look forward to seeing what you do with it and i will continue with posting my works.
My success to the hogs is down to you and others help here, without that help i would still have an unusable gun.... So thanks again!!

Going to give the pigs a couple of more nights and then concentrate on workshop time.

Would love some input on what i intend to do......I am thinking to start by

Full air and chrono down and find out what my reg is set at, currently getting about 820/30fps with the Snowpeak pellets.

Then i want to do something with the "bolt" as it lifts up on shooting and also want to address the weak bolt head stopping us getting the bolt in our face.

Once the gun is safer i want to...

Adjust the reg up a little to get me in the 950fps range.

Then work on the hammer spring, this would be good to get your input as i go, Im thinking to measure my H/spring and if close to what yours measured i think to reduce it down to what you have done, if not a little more.

So with that in mind, think i said before, i want to drill out and tap the hammer spring cap and install a bolt with the bolt head shaved down to a washers thickness for the spring to sit up against and then will have an external adjustable hammer spring... Shaved head of bolt inside cap and threads outside cap with screwdriver flat for adjustment, locking nut if needed once set.

In principle to my mechanic's head this should work but wanted to ask opinions here before i do this, i cant see the hammer spring having enough force when cocked to damage the threads i would tap ??
The cap seems to be pretty thick allowing plenty of threads for security but does anyone have any thoughts on my idea.

Am i missing an easier way to "tune" the M25 than installing my H/spring adjuster idea?

Then if all goes well i will chrono it adjusting fps until i get the best grouping, with JSB exacts this time   and then with my adjustable hammer spring set to 5% below the plateau.

Does this sound like a plan?