Kahr P45 Magazine Capacity Modification

[Bullz]

I'm new to forums in general... Please forgive me if this is discussed somewhere else. I couldn't find anything after 20 minutes of searching...

Anyway, here's the situation:

I have a Kahr P45. The mags have a 6 rd capacity but appear to have physical space enough to support a 7 rd capacity if the mag spring were to be chopped one or two coils. I mean, it easily holds 7 with room to spare without the spring in the mag. A stronger spring with less coils would probably do the job...

Thing is, I'd like to get a 7 +1 capacity out of the normal mags... The existing spring seems like it would be strong enough cycle properly short two coils but I'm not really sure. Has anyone tried this on a Kahr or other single stack pistol? I might just order a couple new mag springs and try it out...

 

[Mizar]

And if you throw away the spring and follower you will be able to put 8 rounds in it!! There might be a good reason for Kahr engineers to design a 6 round magazine...

 

[usp9]

I don't think I'd fiddle with a Kahr mag much, they're fickle enough. Besides, I'm not sure I agree that there's enough room for another round, it's pretty tight in those mags. If you really want another round just get a TP45 mag and live with the length. My advise, leave it alone or buy a bigger mag.

 

[Bullz]

You're both right... I'm sure there's a good reason for it... and I know I can buy an extended round mag... But, I'm looking at this from an engineering stand point and I don't get it. You can get an Officer's Mag that is the same size as the Kahr mag and it holds the extra round. And I can clearly see that the current internal setup of the mag is about 2mm short of being able support the extra round... which is exactly the measurement for two compressed spring coils. Now, i'm not sure how tight it would be or if it would even function...

Anyway... I wanted to see if anyone has toyed with this before I start chopping things up. The extra round isn't that big, from a practical standpoint... but you know how it is... you get an idea to make something "better"....

 

[The Lone Haranguer]

The mags have a 6 rd capacity but appear to have physical space enough to support a 7 rd capacity if the mag spring were to be chopped one or two coils.

And then the spring would no longer have enough power to push the heavy rounds up in time, would be my guess. Chances are Kahr designed the magazine that way for a reason. If you still want to go ahead with it, buy some new springs to cut on - or to have ready for replacement - so your gun isn't disabled.

 

[NG VI]

If you've already got a couple of spare springs on hand, go for it. I wouldn;t try to carry with t he modified magazine until you've tested it retty heavily, but springs usually don't cost too much.

 

[Bullz]

I'm going to get an extra spring at some point and then try it out. I may also see if I can get some officers mag springs and see if they have a different coil count. That's the main issue... if there were half as many coils with twice the strength, it could take the extra round with room to spare. I'm really surprised no one has tried this... I've searched it out but all I see is people trying to get flush fitting mags... oh well. I'll let you know what happens once I get around to it.

 

[Jim Watson]

Thing is, the native capacity of the OACP is, like the P45, six rounds.
They did the same kluge to get in seven as they did to get eight in the full size GM, a shorter follower and a shorter spring. Some of us worry about the reliability and durability of the change.

That said, I have used Wilson 47 eights in IPSC and IDPA. When the skimpy spring starts to get weak(er) it quits lifting the slide stop but still keeps feeding, so I always had a warning to change springs before the gun quits shooting.

 

[K-Rod]

If you can't do it with 6, your in trouble anyways. My advice, don't mess with it & practice fast Mag swap. Lots of guys toting 6 shooters.

 

[bigfatdave]

would an "extra round" in the magazine still allow it to be seated in a closed gun? You still need room for the feed boss on the bottom of the slide

would a shortened spring have the power to lift the last rounds in the mag? better find out with an extra spring, don't chop one up until you get a spare on hand ... not sure if Wolff has extra-power springs for that model, but I'd start there

would the chopped spring sit correctly and maintain feed angle?

 

[Bullz]

yeah, I get it... "if you think you need an extra round, practice more, or carry more mags or whatever..." Not the point here. That logic drives me nuts because it's all a question of where you draw the line. Why not just F it and start carrying around a single shot contender? Who needs extra rounds, right K-rod?

I would just be happy with 7 + 1 in the pistol without an extended mag. The philosophy behind why is irrelevant.

Bigfatdave, it looks like everything will fit just fine without the mag spring in place. The follower on this guns magazines has a large concave space in which most of the spring compresses. The remainder of the spring volume that does not compress within the follower would be equal to the portion to be eliminated. This is where the reduced coil count comes into consideration. Conceptually, it should work fine, but it will really depend on spring strength. I can say, the springs are really tight as is...

Jim Watson, good point on the slide catch. Kahr has a very agressive system so I'm not too concerned with that at this point. I'm anticipating the problem with that as the spring tension might be too light to get in place once the final round goes... we'll see.

I'll check out the wolf springs and I will certainly heed the advice to acquire additional springs before performing any modifications. It's just going to have to be a trial and error thing.

 

[outerlimit]

They did the same kluge to get in seven as they did to get eight in the full size GM, a shorter follower and a shorter spring. Some of us worry about the reliability and durability of the change.

Yep, exactly why the reliable 8rd Government/Commander mags stick out a bit.

I like how you look at things though Bullz, perhaps they can design a (semi-flush) 7rd mag for the Kahr, but it would probably take some design tweeking that would make it less reliable in the field.

 

[Drail]

While it is theoretically possible to do this be assured that spring life will be short by compressing it that much when full. The limit on mag capacity is how far and how many times can you compress the spring that tightly and still have it feed the last round when it is released. There are practical limits to how much compression and expansion a spring will take before you lose the rating you need to get that last round up fast enough to be picked up by the slide. The 6 round Officaer's ACP mag is fairly reliable. The 7 round will lose reliability more quickly as the temper in the spring goes. The follower will need to be something like the McCormick Devel follower that is able to collapse slightly when fully loaded. All of this refers to a magazine body that is flush with the grip frame. If you're willing to extend it anything is possible. Personally the trade offs are not worth one extra round to me.

 

[Jim Watson]

Yep, exactly why the reliable 8rd Government/Commander mags stick out a bit.

Kahr offers a 7 shot .45 magazine that protrudes maybe 3/4 inch.
I guess if you were experimentally minded, you could take one of these, peel off the plastic finger rest, and start putting spacers in the bottom to see just how long a magazine HAD to be to hold 7. Then have it cut and the floorplate reset at that length. Might be like those GM magazines and only stick out 1/8 - 1/4 inch.

 

[Seven For Sure]

I have a P45 and agree it would work. 1/2 a round will fit as is. Try PM45 springs from Wolff. Those are what Kahr uses for mag, recoil and maybe other springs as well? I'll order a couple and guinea pig it for us. If it won't work I'll have new PM45 springs for sale cheap!

 

[RedAlert]

My Kahr PM40 has an offset feed path. Does your Kahr have one too? This is a design feature to facilitate the trigger mechanism. The Kahr triggers are quite good for DAO.

I'd suggest the stout spring is a design to assure proper feeding of the round. After all, the short recoil combined with the offset feed path require a positive push from the mag spring to move the round into the chamber.

 

[gb6491]

Bullz,
Kahr 6. rd. magazines will feed reliably with components from 7rd. Officer's magazines. The problem is (as mentioned above) getting the slide to lock back.
My intention when I first started experimenting with the CW45 mags was to find something that would fit flush and increase capacity. The flush fit part worked out very well: Officer's/compact 1911 magazines can be can easily be modified to fit and function reliably in the CW45. However, getting them to lock the slide back proves a challenge. With one exception, none of the Officer's mags I tried had a follower that would lock the slide back. Unfortunately, their springs will not work with the Kahr follower. Fortunately, the Kahr follower and spring works just fine in Officer's mag tubes, so I had my flush fit mags. About the one exception, Mec-Gar makes an Officer's size, 6 rd. mag that has a follower and spring combo that will lock the Kahr slide back after modifications to the tube are done. This is about the least expensive, viable way to go for a CW45 magazine as these magazine run in the $14-$20 range. With that all said, a fella posted in this long thread on Kahr Talk that he was able to bend the follower in a Kimber 7 rd. compact magazine and get it to function correctly (to include lock back). I didn't get the same results, but thought I'd throw that out there.
My CW45:

Regards,
Greg

 

[wally]

My take. If the mags are only for range use, go for it, all you risk is a spring.

OTOH for carry mags, IMHO the odds of that extra round saving your life is about 1/6th the odds of it costing your life with a feed failure.

With enough failure free range use, I might trust it but only if left fully loaded between sessions as a carry mag would be. What you are not going to be able to test is the jostling and FOD (lint, dead skin, moisture cycles from sweat, etc.) your carry mags will experience.

 

[NG VI]

Sure he can, all he has to do is carry it around in a pocket or in an extra mag carrier. I wouldn't carry it as my only spare magazine, but to help prove the magazine, why not toss it in your pocket for a few weeks before shooting it again?

 

[chris in va]

Whatever happened to the helical coil spring concept? IIRC they compressed flat in the mag, taking up very little space.

 

[Bullz]

Lots of great posts. Thanks a lot guys. It's a big help. I've decided that I'm going to go ahead with the project but I'm going to order some dummy springs to chop rather than modify the stock springs.

A few points I want to respond to...

Drail, you're right about the spring life. All springs are subject to failure given an expected useful life. However, I think these pistol mag springs are more resilient than people think. The springs in your car undergo thousands of short burst compression cycles every trip you take... albiet, not the same thing as a pistol mag spring but the technology is similar... That said, durability is less of a concern than performance. Additionally, if the mag holds 7 rounds and only feeds 6 of them reliably then I'm really no worse off, am i? If the last round doesn't feed, I still got the same 7 shots off that I would have otherwise. This is also going on the broad assumption that the other rounds feed reliably. But that's what range testing is for.

GB6491 - Thanks for the picture and info. The setup looks perfect. If I get this capacity conundrum resolved, the flush floor plate will be the next attempt at aligning this pistol with my vision. I really really like what I'm seeing. It looks like a little bit of machining could probably get the follower issue resolved.

Wally - valid point and concern. The modified springs will undergo several hundred rounds of testing before I start toting them around. I'm intimately familiar with the operations of this pistol and I can tell you with a great degree of certainty that any problem with the feed operation post spring modification will present itself within the first testing run.

Chris in va - I don't know anything about these helix coil springs. I'm trying to imagine them but I can't figure how a helix would offer any space savings from a compression standpoint. I can see how they may offer a more uniform compression pattern, though. Do you have any information or links with regard to this concept?

 

[GLOOB]

would an "extra round" in the magazine still allow it to be seated in a closed gun? You still need room for the feed boss on the bottom of the slide

Did you read this? I've had the same sort of idea before. I hope you have better luck than I.

1/2 a round will fit as is.

And so, you might need room to stuff another round in, plus up to 1/2 a round extra.

 

[Bullz]

This is true. Now... what I did for a rough test on this issue was simply assemble the mag without the spring, load it full (with 7 rounds) and seat it both against the closed slide and and open slide. With 7 rounds and no spring, the rounds are just hanging out in there with plenty of room. I've determined that if it is possible, the answer is all in the spring... either modified or some aftermarket piece that is stronger with less coils.

 

[9mmepiphany]

It sounds like an interesting experiment, please keep us informed as to the results you come up with.

When you start playing with spring rates, you start affecting the timing of the action, by upsetting the balance between the three springs. There is a built in margin for reliability and manufacturing tolerance. They also have to take into account the acceptable frequency, by the customer, for spring replacement. I've seen guns (Wilson ADP) that required spring replacement at about 500 rounds...which folks found unacceptable

It isn't something I would do on a gun I would carry for serious work, but I am curious about it's functionality. Kahrs are already pretty much on the edge of how compact you can make a reliable gun...see their patented feedramp and their instruction to use the slide stop to release the slide...and they did a lot of work trying to make sure their guns don't hiccup at the wrong time. The first priority of a gun you'd carry has to be reliability

 

[Bullz]

9mmepiphany, good points of concern. I'll keep my eye on all of these things listed here... you guys are a big help. By the way... what's your tag in reference to?