Wildcatting: Fire to Air

I love airguns, I love firearms; so; what would be better than to combine the two? So, your 308 or any 30 cal rifle can be converted to shoot airgun pellets for some short-range fun! Sub-sonics are one thing, but these midget lightweight projectiles are a different ball game. Trying to get a lightweight 30 cal bullet is problematic, I have used to good effect Hornady’s 90-grain XTPs for moderated fox use, but they can be a little rifling sensitive.

All low velocity rounds have their own foibles in terms of what they like or dislike when being reloaded. To me, that’s half the fun, trying to get all the primers, powder, neck tension etc just right for a round that works. Obviously, the first thought is how the hell can an airgun pellet fit into a 308 case? Well for .177, .20, .22 and .25 cals a sabot casing is needed, although some actual .30 cal airgun pellets i.e. JSB for the mighty Daystate Wolverine have their uses.

What you need

Sabots are the way to go and this involves sourcing them; true, a bit hard these days, but internet types will be able to find some, and Arms Fairs turn up quite a few. I have a stash from E Arthur Brown Company from the USA and a friendly CNC chap that can turn up a few oddities too!

If you are handy on a lathe it is not that difficult to make a calibre-specific sabot to fit your needs or projectile. I use Teflon, Nylon or Delrin but the purpose is the same. The idea is that the actual projectile is surrounded by a bore diameter outer divided into a number of sections, that allows it to ride the bore then separates as it exits. The actual word is French and means a wooden shoe. In this way, you can fire lighter, sub-calibre bullets to achieve higher velocities.

Here, I am just trying to produce some short-range vermin/fun lead pellet options to see if it works really. The Brown sabots are grey coloured with a 0.308” groove diameter and 0.537” long with six serrated petals that fold back to release the bullet in flight. There is a slight dip to the base to aid in obturation and the bullet recess is 0.430” deep and has an internal diameter of 0.2170”, so good for 0.224” bullet or pellet.

Bumped

The trouble is that with most of the lighter airgun pellets, the overall length is too short to be securely held by the sabot. Here some wadding or judicious pellet selection, as well as a hot glue gun adhesive or super glue cures this issue. Here is where you need to think about some sort of adhesion and whether you are trying to achieve separation of pellet and sabot after leaving the barrel or intend shooting both as a single entity. Correct primer choice is paramount, because with a sabot you have two projectiles of different weights/masses, so inertia from the heavier projectile will want to leave the lighter sabot. What can happen is that primers force will ‘bump’ the pellets out of the sabot and that’s not good for accuracy.

I use Federal 210 primers, as from experience with my loads they seem to be the most consistent for sabot use, but feel free to experiment. Also, it is a consideration that loading the sabot backward to be used as a 30 cal Wadcutter does have its merits and it can be used stand alone or loaded with a wad or pellet to increase its weight and thus momentum. (See Results)

NB: - I started with a load of 2-grains of Trailboss, as it’s fast burning and very bulky too, for its weight, so ideal for small charges that fill the case a bit better.

There is a central hole in the powder disc to improve an efficient burn. As always with small charges and big cases, the charge lies flat in the case when the rifle is shouldered, I raised the gun to get the powder over the primer before firing to aid in consistent ignition.

2-grains of Trailboss was OK for the Tac1’s 20” barrel, as all left the barrel, but on the RPA 24” tube the sabot got stuck an inch or two from the muzzle. Therefore, I upped the charge to 3-grains and all fully exited at 1045fps just to be safe. Loading it backward caused the petals to open and grip the bore, so causing it to slow down and not seal correctly, damn!

Now by adding each projectile at a time I wanted to see the velocity only at this stage. Would the primer ignition bump the pellet out of the sabot, get stuck, or would both elements stay in perfect union?

Pondering

Well, as with all experimenting, it throws up some interesting conundrums to ponder. With sabots, projectile fit is key, as I had some separations that resulted in it lodging an inch from the muzzle and the pellet barely making it over the chronograph. And as the bolt was opened, a nice pressure release of exhaust gas was heard. This happened with the lighter pellets, as the weight of the projectile allowed the primer to move the sabot and literally bump its lighter, looser fitting payload from its grip and so lost a lot of forward momentum and became stuck. This happened to the RWS Hyper, H&N Hyper Max and Sniper Light. The H&N FTTs, although light, were a good fit and so fired fine. The H&N Hornet also shot well with only 2-grains of Trailboss at 557 fps and then with 3-grains at 870 fps; it just shows.

As can be seen, there was a huge disparity in velocity between pellets fired. Those with the greatest mass, largely, achieved better velocities and allowed a good back pressure and build-up of the Trailboss burn generating healthy velocities. Although the Hyper Domes were light but a good fit.

Various

The Barracuda Greens shot a nice, consistent but low 678 fps, whilst the Eley Magnums were a lovely fit as expected shot 1014 fps velocities. Best or highest speed went to the RWS HyperDome with the same 3-grains of Trailboss, as they were a good fit to the sabot and achieved a mighty 1334 fps. The Emperor 30 cals were hard to get seated as expected, as only a neck diameter on the case of 0.3065” or a slight crimp would get consistent results at 886 fps. Leave for another time. The old Daystate Varminter HP gave good velocities but 3”+ groups! The Sussex Armoury sabots will have to wait to another time too, as I’m running out of space.

Accuracy was ‘subjective’ is probably the polite way to say this! Obviously, the loose or lower velocity pellets were inconsistent and at 25 yards were 2-3” at best. Often the sabot would hit the paper too, but most separated cleanly from the pellet along the route, with the carrier staying largely intact.

Best or what?

The best accuracy came with the HyperDomes, Eley Magnums, and Hornet pellets. The Domes were a real surprise, as they gave 1” groups at 30 yards with full separation and often the sabot hitting the target sometimes on top of the strike. The Eley’s actually stayed together at 30 yards, they were a tight fit and grouped 3-shots at 30 yards into 0.75-1.0” but sometimes yawing a bit on entry.

The Hornets separated somewhere past the chronograph and made some nice 0.75-1.0” groups, but often two pellets in 0.50” and the other off - encouraging. I had a very surprised rat at 25 yards that came out for some sweet corn with a Hyper Dome pellet strike, followed by a sabot hit too!

Conclusions

I was using some light pellets to see how fast I could go really; so, next time I will switch to heavier types with a better fit for best results. That’s what I like, you never really know until you try something, practical uses are very limited but just a fun way to experiment. although that rat would beg to differ!

Contacts

Norman Clark Ltd Reload Supplies – 01788 579651
JMS Sporting Quickload ballistic program 07771 962121 www.quickload.co.uk
Edgar Brothers Powder – 01625 613177
John Rothery Pellets – 023 9224 5350
Hannams Reloading Lapua cases – 01977 681639
GMK Ltd Tikka rifles – 01489 579999