Benjamin Marauder magazine pellet alignment

[Earthworm]

I’ve been chasing accuracy issues on my stock Marauder in .25.  Single loading, I can comfortably make groups well under 3/4 inch at 25 yards (H&N Barracuda Hollowpoints at 28.24gr).  Loading from the magazine, the groups are all around an inch, with some worse than that- the pellets that needed more force seeming to be least accurate, up to 2-inch groups.

I did a the magazine cleanup from the Hajimoto productions video, but on closer inspection, what seems to be happening is that the magazine is presenting the pellet to the breech too low- pellets that take too much effort to chamber wind up with a “smile” across the bottom, where they were smashed up against the “feed ramp” of the lower edge of the bore.

I’ve shimmed the magazines upward by placing three layers of painters tape on the bottom, so they sit a little higher, and this improves things.  I did try a little strip of painters’ tape inside the magazine on the ‘stop’ that pellets are rotated up against, but there isn’t a whole lot of room for them to come out, and this cuts that exit off.

My other observation is that the breech face doesn’t protrude too far into the action area- certainly not as far as the cutout on the magazines would allow.  The pellets thus have to be pushed across a 2mm or so gap to get  in the ‘chamber.’ They seem to be under pretty positive control, and not wobbling or anything, but perhaps the barrel needs to be adjusted backward?

Is there any chamber treatment that typically needs doing on a stock marauder?  Polishing the ‘feed ramp’/edge of breech?  Actual changes to its contour?  Is this a magazine problem?  I suspect that there’s some variance based on what position in the magazine the pellet came from, but I haven’t tested that.  I suppose different pellets might have an easier time of it, but I use this setup for pest control, so not sure domed pellets are the solution, and, for ethical reasons, I’d really like to use the magazine to have an accurate follow-up shot immediately available.

Am I even asking the right questions?  I’m pretty new to this sport and to the Marauder, so it’s likely that there are sources of inaccuracy I don’t even know to look for.  Where should I start?

[Grumpy Old Man]

 I am just an old powder burner and being new to PCPs, I don't know much about them. I can tell you that if a bullet enters a barrel at an angle, It will exit at an angle. That's why head space is so important on a center fire.  My new 22 Mrod is throwing flyers no matter how I adjust it. I Pulled the barrel and pushed a pellet through. There is a tight spot just past the transfer port that is probably causing my problem, So I'm going to lap the barrel, IMHO the plastic magazine is a POS, looks like it belongs in a child's toy. Moving the barrel back might help but I'm not sure what that would do to your transfer port alignment. I would be interested in how you make out. Good Luck

[RichH]

Do you just have a single magazine? Or is it multiple mags? The Marauder mag is designed to fit the barrel, the section of barrel that extends beyond the receiver, so shimming it from the bottom should only cause it to be harder to insert. It works off the premise that the bore is centered in the barrel and the hole in magazine is centered in the "retaining" groove. You can always put a bit more chamfer on the leade. This should allow for easier chambering of the pellet.

[HunterWhite]

Perhaps the bore is not concentric with the outer diameter of the barrel.
I recall reading that sometimes changing the caliber can cause the misalignment between the magazine and the bore.
If I have this problem,  I've never noticed it.
Hopefully someone can give more specific information.

Hunter

[AlanMcD]

I have never had any issue with multiple mags in both .22 and .25 cal on my Marauders - I find them all to be equal to each other, as well as single shot loading.  It it one of the things I have really liked about the platform.

What Rich said is dead on - the mag actually "attaches" to the barrel by a friction fit, and all the slot in the breech block does is keep it in the right place, mostly fore-aft so it does not fall off the barrel.  In fact, if you had the barrel out of the gun, you would be able to fit the breech on the barrel and it would stay on its own.

I suspect that you either have a bad magazine, or what Hunter said is true - a problem with concentricity in your barrel (as the mag attaches to the outside of the barrel, on the small bit that extends into the breech.

Is the gun new?  If so, it might be worth contacting Crosman.  If not (or first) you could try another mag - at least they are cheap.

The only time I have experienced difficult loading as you describe was when the breech seal o-ring came out once, but that also led to a louder shot so it was easy to figure out what happened.  It was putting that "smile" on the pellets from the groove in the barrel.  I did not try single loading like that, but it clearly was damaging the pellets.  A replaced o-ring put everything back to normal.

Here is a picture I just took of a .22 mag on the end of a stock .22 barrel that I have that is not in a gun.  Note that picture is oriented as I was holding it, with the barrel up and the mag down, and it does not fall off.

[HunterWhite]

Good point Alan, the O-ring. I forgot about that. The only time I've replaced one was because I had the barrel out of the rifle to inspect the transfer port. I was cleaning the barrel and forgot the little O-ring was there, luckily I had a spare.
I don't know how easy it is to replace with the barrel still in the breech.

Hunter

[bear air]

They can be a PITA replacing them with the barrel on the gun. I like to use a small dowel and picks when the barrel is still on the gun. It is much easier to pull the barrel and replace the oring though. To the OP, you might think about polishing the lead of your barrel. I have a new barrel I just put on my brod and I opened up the port yesterday and polished the lead really good. I noticed the pellets were loading much easier now. I had a gen 1 stormrider that had such a horrible lead that I actually had to use a dremel and open it up to be able to use the mags. Good luck and hopefully you get it sorted out.

[Frank in Fairfield]

I put the new o-ring (Well lubed) on the probe and close the probe.
Voila

[triggertreat]

I agree with what has already been said by other members.  I have seven mags for my .25 cal Synrod and haven't had any issues with them, and groups appear the same as with an SST.

There is a little wiggle room within the TP for the barrel to slide back and forth to set the mag tension.  I like my mags to fit snug with a little effort required to snap them into place, but not with too much binding going on either.

If your mag is not cut to spec, I could see having some issues.  I don't think a loose or a tight mag within the range allowed by the TP is going to make much of a difference being the mag snaps over the barrel end for alignment to begin with.

Added: You can use a 1/4" dowel rod and some JB bore paste on the leade-in for smoother loading.  Pull the barrel and you can push/ram the dowel into the leade and just slightly into the bore to shape the dowel then apply some JB bore paste or something to polish metal with. Run the rod back and forth a number of times within the lead and leading edge of the lands and then clean up and check how it's feeling and if more is needed. There are other methods that may be better, but this is how I chose to polish my leade for loading tight fitting slugs.  It worked very well for me.

[SpeedyBB]

Have you tried loosening the barrel grub screws and adjusting it to a magazine for a perfect fit then re-tighten? Note it can't move much with the transfer port, so the breech (receiver) needs to come off and transfer port removed to do this really proper. Anytime I am installing/re-installing a barrel on mine I do this to ensure proper magazine fit. Also make sure the transfer port hole is lined up.

[Earthworm]

Sooo...

I had initially skimmed over the the discussion of the o-rings, because I haven't done anything to mine.  But I eventually looked, and there was no o-ring there!  It was hanging out on the bolt in the back of the receiver...  (this may explain why single loading was louder than using the magazine)

I should be able to get that back in place and test this afternoon.  However, I'm still concerned about the magazine alignment- they fit in too loosely (I'd have never imagined that they'd stick on to the end of a barrel, for instance), and the fact remains that the pellet is aligned at a millimeter or so below the bore axis- having an o-ring to bump over will be better than a steel edge, but going straight in should be better.

How far is the barrel supposed to protrude into the action area?  Is that a thing that could change/be maladjusted?  I have not messed around with it, but the protrusion is around 0.5mm/less than 1/32in (that's based on a steel ruler held at an angle, me having lent out my calipers).

[bear air]

You can loosen the two barrel set screws in the breech, put a transfer port in the breech/barrel, then take a magazine and insert it into the breech. There is a little wiggle room there to let the mag snap in nice and tight while keeping the TP in alignment. Then once everything is where you want it cinch down the barrel set screws. Hope this helps. Installing a barrel oring will also quiet the gun down and gain you velocity.

[KevinJBrown]

This thread has given me a lot of food for thought. Every so often I get a pellet that makes more noise than usual going into the barrel; every so often I get a pellet that takes more effort than usual, and every so often I get a bit of a flier. I wonder if this could have something to do with the pellet entry into the barrel.

I do have a question for the long time Marauder shooters, and that is how often do you change the barrel o-ring?

Thanks

[HunterWhite]

I like to insert the barrel into the receiver while keeping the transfer port of the barrel aligned with the hole in the receiver. Then I test fit the magazine.  It should be close, but it could be adjusted a little.

Hunter

[SpeedyBB]

If your mags are loose the barrel just needs backed up a little, and that should also keep things aligned better when loading pellets.

[triggertreat]

This thread has given me a lot of food for thought. Every so often I get a pellet that makes more noise than usual going into the barrel; every so often I get a pellet that takes more effort than usual, and every so often I get a bit of a flier. I wonder if this could have something to do with the pellet entry into the barrel.

I do have a question for the long time Marauder shooters, and that is how often do you change the barrel O-ring?

Thanks

About 4-5 times per year minimum.  Basically every time I clean the barrel really good instead of just using a bore snake.  If I used a poly O-ring that would change to far less replacements, but I like the NBR 70 for loading past.  There's simply no substitute for a good O-ring in the breech.  The ES is much more consistent and the gun is the quietest it can get with a good ring in place.

Just load a pellet/slug just barely past the O-ring groove.  If needed, insert a wood dowel or cleaning rod from the muzzle end to keep that pellet right at the grove.  Now you can lube an O-ring and push it into place using the projectile to prevent the ring to go beyond that grove.  With practice it can become a simple and quick task.

[Vee3]

I do have a question for the long time Marauder shooters, and that is how often do you change the barrel o-ring?

I change it every time I accidentally pull the trigger with the bolt to rear, in cocked condition. Why? Because when I do that, the O-ring blows out and vanishes every time. 

[HunterWhite]

I change it every time I accidentally pull the trigger with the bolt to rear, in cocked condition. Why? Because when I do that, the O-ring blows out and vanishes every time. 

Okay, an easy way to remove the old one!
Thanks!

[KevinJBrown]

OK, next question(s) what is a good source for the O-ring (and what are the different options) in question?